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  • 251.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    MOCVD growth of GaN-based high electron mobility transistor structures2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present work was to improve the overall quality of GaN-based high electron mobility transistor (HEMT) epitaxial structures grown on semi-insulating (SI) SiC and native GaN substrates, using an approach called bottom-to-top optimization. The bottom-to-top optimization means an entire growth process optimization, from in-situ substrate pretreatment to the epitaxial growth and then the cooling process. Great effort was put to gain the understanding of the influence of growth parameters on material properties and consequently to establish an advanced and reproducible growth process. Many state-of-the-art material properties of GaN-based HEMT structures were achieved in this work, including superior structural integrity of AlN nucleation layers for ultra-low thermal boundary resistance, excellent control of residual impurities, outstanding and nearly-perfect crystalline quality of GaN epilayers grown on SiC and native GaN substrates, respectively, and record-high room temperature 2DEG mobility obtained in simple AlGaN/GaN heterostructures.

    The epitaxial growth of the wide bandgap III-nitride epilayers like GaN, AlN,  AlGaN, and InAlN, as well as various GaN-based HEMT structures was all carried out in a hot-wall metalorganic chemical vapor deposition (MOCVD) system. A variety of structural and electrical characterizations were routinely used to provide fast feedback for adjusting growth parameters and developing improved growth processes.

    List of papers
    1. Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface
    Open this publication in new window or tab >>Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface
    Show others...
    2015 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 428, p. 54-58Article in journal (Refereed) Published
    Abstract [en]

    The crystalline quality of AlGaN/GaN heterostructures was improved by optimization of surface pretreatment of the SiC substrate in a hot-wall metal-organic chemical vapor deposition reactor. X-ray photoelectron spectroscopy measurements revealed that oxygen- and carbon-related contaminants were still present on the SiC surface treated at 1200 °C in H2 ambience, which hinders growth of thin AlN nucleation layers with high crystalline quality. As the H2 pretreatment temperature increased to 1240 °C, the crystalline quality of the 105 nm thick AlN nucleation layers in the studied series reached an optimal value in terms of full width at half-maximum of the rocking curves of the (002) and (105) peaks of 64 and 447 arcsec, respectively. The improvement of the AlN growth also consequently facilitated a growth of the GaN buffer layers with high crystalline quality. The rocking curves of the GaN (002) and (102) peaks were thus improved from 209 and 276 arcsec to 149 and 194 arcsec, respectively. In addition to a correlation between the thermal resistance and the structural quality of an AlN nucleation layer, we found that the microstructural disorder of the SiC surface and the morphological defects of the AlN nucleation layers to be responsible for a substantial thermal resistance. Moreover, in order to decrease the thermal resistance in the GaN/SiC interfacial region, the thickness of the AlN nucleation layer was then reduced to 35 nm, which was shown sufficient to grow AlGaN/GaN heterostructures with high crystalline quality. Finally, with the 35 nm thick high-quality AlN nucleation layer a record low thermal boundary resistance of 1.3×10−8 m2 K/W, measured at an elevated temperature of 160 °C, in a GaN-on-SiC transistor structure was achieved.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Heat transfer; Metalorganic chemical vapor deposition; Nitrides; High electron mobility transistors
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117132 (URN)10.1016/j.jcrysgro.2015.07.021 (DOI)000360501200009 ()
    Available from: 2015-04-17 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
    2. Impact of residual carbon on two-dimensional electron gas properties in AlxGa1−xN/GaN heterostructure
    Open this publication in new window or tab >>Impact of residual carbon on two-dimensional electron gas properties in AlxGa1−xN/GaN heterostructure
    2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 19, p. 193506-Article in journal (Refereed) Published
    Abstract [en]

    High tuneability of residual carbon doping is developed in a hot-wall metalorganic chemical vapor deposition reactor. Two orders of temperature-tuned carbon concentration, from ∼2 × 1018 cm−3 down to ∼1 × 1016 cm−3, can be effectively controlled in the growth of the GaN buffer layer. Excellent uniformity of two-dimensional electron gas (2DEG) properties in AlxGa1−xN/AlN/GaN heterostructure with very high average carrier density and mobility, 1.1 × 1013 cm−2 and 2035 cm2/V·s, respectively, over 3" semi-insulating SiC substrate is realized with the temperature-tuned carbon doping scheme. Reduction of carbon concentration is evidenced as a key to achieve high 2DEG carrier density and mobility.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-96138 (URN)10.1063/1.4804600 (DOI)000320440800103 ()
    Available from: 2013-08-14 Created: 2013-08-14 Last updated: 2017-12-06
    3. Room-Temperature mobility above 2200 cm2/V.s of two-dimensional electron gas in a sharp-interface AlGaN/GaN heterostructure
    Open this publication in new window or tab >>Room-Temperature mobility above 2200 cm2/V.s of two-dimensional electron gas in a sharp-interface AlGaN/GaN heterostructure
    Show others...
    2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 25, article id 251601Article in journal (Refereed) Published
    Abstract [en]

    A high mobility of 2250 cm2/V·s of a two-dimensional electron gas (2DEG) in a metalorganic chemical vapor deposition-grown AlGaN/GaN heterostructure was demonstrated. The mobility enhancement was a result of better electron confinement due to a sharp AlGaN/GaN interface, as confirmed by scanning transmission electron microscopy analysis, not owing to the formation of a traditional thin AlN exclusion layer. Moreover, we found that the electron mobility in the sharp-interface heterostructures can sustain above 2000 cm2/V·s for a wide range of 2DEG densities. Finally, it is promising that the sharp-interface AlGaN/GaN heterostructure would enable low contact resistance fabrication, less impurity-related scattering, and trapping than the AlGaN/AlN/GaN heterostructure, as the high-impurity-contained AlN is removed.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2015
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117133 (URN)10.1063/1.4922877 (DOI)000357036600005 ()
    Available from: 2015-04-17 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
    4. Growth optimization of AlGaN/GaN HEMT structure on 100 mm SiC substrate: Utilizing bottom-to-top approach
    Open this publication in new window or tab >>Growth optimization of AlGaN/GaN HEMT structure on 100 mm SiC substrate: Utilizing bottom-to-top approach
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The structure of high electron mobility transistors (HEMTs) based on group-III nitride materials generally consists of three important blocks; a nucleation layer, a semi-insulating (SI) GaN buffer layer, and active layers. In this work, we present an overall growth optimization, which leads to superior crystalline quality and ultra-low thermal boundary resistance (TBR) of a 35-nm AlN nucleation layer, excellent crystalline quality of carbon-doped GaN buffer layer, and high mobility (> 2000 cm2/Vs) of two-dimensional gas (2DEG) in a simple AlGaN/GaN heterostructure grown on a SI SiC substrate.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117134 (URN)
    Available from: 2015-04-17 Created: 2015-04-17 Last updated: 2015-04-17Bibliographically approved
    5. Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates
    Open this publication in new window or tab >>Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates
    2015 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, article id 085301Article in journal (Refereed) Published
    Abstract [en]

    Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H2 atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm2/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 1020 cm−3 at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm2 SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP), 2015
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117135 (URN)10.1063/1.4913223 (DOI)000351132500059 ()
    Note

    The authors would like to acknowledge the support from the Swedish Foundation for Strategic Research.

    Available from: 2015-04-17 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
    6. Dispersive Effects in Microwave AlGaN/AlN/GaN HEMTs With Carbon-Doped Buffer
    Open this publication in new window or tab >>Dispersive Effects in Microwave AlGaN/AlN/GaN HEMTs With Carbon-Doped Buffer
    Show others...
    2015 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 62, no 7, p. 2162-2169Article in journal (Refereed) Published
    Abstract [en]

    Aluminium gallium nitride (AlGaN)/GaN high-electron mobility transistor performance is to a large extent affected by the buffer design, which, in this paper, is varied using different levels of carbon incorporation. Three epitaxial structures have been fabricated: 1) two with uniform carbon doping profile but different carbon concentration and 2) one with a stepped doping profile. The epitaxial structures have been grown on 4H-SiC using hot-wall metal-organic chemical vapor deposition with residual carbon doping. The leakage currents in OFF-state at 10 V drain voltage were in the same order of magnitude (10-4 A/mm) for the high-doped and stepped-doped buffer. The high-doped material had a current collapse (CC) of 78.8% compared with 16.1% for the stepped-doped material under dynamic I-V conditions. The low-doped material had low CC (5.2%) but poor buffer isolation. Trap characterization revealed that the high-doped material had two trap levels at 0.15 and 0.59 eV, and the low-doped material had one trap level at 0.59 eV.

    Place, publisher, year, edition, pages
    IEEE Press, 2015
    Keywords
    Gallium nitride, HEMTs, trap levels, current collapse, dispersion
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117136 (URN)10.1109/TED.2015.2428613 (DOI)000356457900014 ()
    Available from: 2015-04-17 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
    7. Impact of AlGaN/GaN interface sharpness on HEMT performance
    Open this publication in new window or tab >>Impact of AlGaN/GaN interface sharpness on HEMT performance
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The impact of the design and sharpness of the AlGaN/GaN interface in GaN-based HEMTs is investigated. Three structures with different AlGaN/GaN interface properties were grown with hot-wall MOCVD. One structure has a 2-nmthick AlN exclusion layer in between the AlGaN and the GaN, while the other two differ in their sharpness of the Al transition at the AlGaN/GaN interface. The structures with AlN exclusion layer and optimized sharpness of the interface show similar electron mobilities (1760 and 1740 cm2/Vs). HEMTs were processed and evaluated. Gated Hall-measurements indicate that the sharper interface maintains a higher mobility when the electrons are close to the interface compared both to the AlNexclusion layer and the non-optimized structure. The higher mobility manifests as lower parasitic resistance yielding better DC and high frequency performance. Pulsed IV measurements indicate that the sharper interface provide less dispersive effects compared both to the AlN exclusion layer and the optimized interface.

    Keywords
    GaN HEMT, AlGaN/GaN interface, sharpness
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117137 (URN)
    Available from: 2015-04-17 Created: 2015-04-17 Last updated: 2015-04-17Bibliographically approved
  • 252.
    Chen, Jr-Tai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Impact of residual carbon on two-dimensional electron gas properties in AlxGa1−xN/GaN heterostructure2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 19, p. 193506-Article in journal (Refereed)
    Abstract [en]

    High tuneability of residual carbon doping is developed in a hot-wall metalorganic chemical vapor deposition reactor. Two orders of temperature-tuned carbon concentration, from ∼2 × 1018 cm−3 down to ∼1 × 1016 cm−3, can be effectively controlled in the growth of the GaN buffer layer. Excellent uniformity of two-dimensional electron gas (2DEG) properties in AlxGa1−xN/AlN/GaN heterostructure with very high average carrier density and mobility, 1.1 × 1013 cm−2 and 2035 cm2/V·s, respectively, over 3" semi-insulating SiC substrate is realized with the temperature-tuned carbon doping scheme. Reduction of carbon concentration is evidenced as a key to achieve high 2DEG carrier density and mobility.

  • 253.
    Chen, Jr-Tai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology. Classic WBG Semiconductors AB, LEAD, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth optimization of AlGaN/GaN HEMT structure on 100 mm SiC substrate: Utilizing bottom-to-top approachManuscript (preprint) (Other academic)
    Abstract [en]

    The structure of high electron mobility transistors (HEMTs) based on group-III nitride materials generally consists of three important blocks; a nucleation layer, a semi-insulating (SI) GaN buffer layer, and active layers. In this work, we present an overall growth optimization, which leads to superior crystalline quality and ultra-low thermal boundary resistance (TBR) of a 35-nm AlN nucleation layer, excellent crystalline quality of carbon-doped GaN buffer layer, and high mobility (> 2000 cm2/Vs) of two-dimensional gas (2DEG) in a simple AlGaN/GaN heterostructure grown on a SI SiC substrate.

  • 254.
    Chen, Jr-Tai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hsu, Chih-Wei
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 8, article id 085301Article in journal (Refereed)
    Abstract [en]

    Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H2 atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm2/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 1020 cm−3 at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm2 SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

  • 255.
    Chen, Jr-Tai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hsu, Chih-Wei
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Persson, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Room-Temperature mobility above 2200 cm2/V.s of two-dimensional electron gas in a sharp-interface AlGaN/GaN heterostructure2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 25, article id 251601Article in journal (Refereed)
    Abstract [en]

    A high mobility of 2250 cm2/V·s of a two-dimensional electron gas (2DEG) in a metalorganic chemical vapor deposition-grown AlGaN/GaN heterostructure was demonstrated. The mobility enhancement was a result of better electron confinement due to a sharp AlGaN/GaN interface, as confirmed by scanning transmission electron microscopy analysis, not owing to the formation of a traditional thin AlN exclusion layer. Moreover, we found that the electron mobility in the sharp-interface heterostructures can sustain above 2000 cm2/V·s for a wide range of 2DEG densities. Finally, it is promising that the sharp-interface AlGaN/GaN heterostructure would enable low contact resistance fabrication, less impurity-related scattering, and trapping than the AlGaN/AlN/GaN heterostructure, as the high-impurity-contained AlN is removed.

  • 256.
    Chen, Jr-Tai
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pomeroy, James W.
    Center for Device Thermography and Reliability, H.H. Wills Physics Laboratory, University of Bristol, UK.
    Rorsman, Niklas
    Microwave Electronics Laboratory, MC2, Chalmers University of Technology, Göteborg, Sweden.
    Xia, Cha
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kuball, Martin
    Center for Device Thermography and Reliability, H.H. Wills Physics Laboratory, University of Bristol, UK.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface2015In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 428, p. 54-58Article in journal (Refereed)
    Abstract [en]

    The crystalline quality of AlGaN/GaN heterostructures was improved by optimization of surface pretreatment of the SiC substrate in a hot-wall metal-organic chemical vapor deposition reactor. X-ray photoelectron spectroscopy measurements revealed that oxygen- and carbon-related contaminants were still present on the SiC surface treated at 1200 °C in H2 ambience, which hinders growth of thin AlN nucleation layers with high crystalline quality. As the H2 pretreatment temperature increased to 1240 °C, the crystalline quality of the 105 nm thick AlN nucleation layers in the studied series reached an optimal value in terms of full width at half-maximum of the rocking curves of the (002) and (105) peaks of 64 and 447 arcsec, respectively. The improvement of the AlN growth also consequently facilitated a growth of the GaN buffer layers with high crystalline quality. The rocking curves of the GaN (002) and (102) peaks were thus improved from 209 and 276 arcsec to 149 and 194 arcsec, respectively. In addition to a correlation between the thermal resistance and the structural quality of an AlN nucleation layer, we found that the microstructural disorder of the SiC surface and the morphological defects of the AlN nucleation layers to be responsible for a substantial thermal resistance. Moreover, in order to decrease the thermal resistance in the GaN/SiC interfacial region, the thickness of the AlN nucleation layer was then reduced to 35 nm, which was shown sufficient to grow AlGaN/GaN heterostructures with high crystalline quality. Finally, with the 35 nm thick high-quality AlN nucleation layer a record low thermal boundary resistance of 1.3×10−8 m2 K/W, measured at an elevated temperature of 160 °C, in a GaN-on-SiC transistor structure was achieved.

  • 257.
    Chen, Ruei-San
    et al.
    National Taiwan University of Science and Technology, Taiwan.
    Tang, Chih-Che
    Department of Electronic Engineering, National Taiwan University of Science and Technology, Taiwan.
    Hsiao, Ching-Lien
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Holtz, Per Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Electronic transport properties in aluminum indium nitride nanorods grown by magnetron sputter epitaxy2013In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 285, p. 625-628Article in journal (Refereed)
    Abstract [en]

    The electronic transport properties of the wide-bandgap aluminum indium nitride (AlInN) nanorods (NRs) grown by ultrahigh-vacuum magnetron sputter epitaxy (MSE) have been studied. The conductivities of the ternary compound nanostructure locates at the value of 15 Q-1 cm -1, which is respectively one and two orders of magnitude lower than the binary GaN and InN counterparts grown by chemical vapor deposition (CVD). The very shallow donor level/band with the activation energy at 11 + 2 meV was obtained by the temperature-dependent measurement. In addition, the photoconductivity has also been investigated. The photoconductive (PC) gain of the NRs device can reach near 2400 under a low bias at 0.1 V and the light intensity at 100W m-2 for ultraviolet response in vacuum. The power-insensitive gain and ambience-dependent photocurrent are also observed, which is attributed to the probable surfacecontrolled PC mechanism in this ternary nitride nanostructure.

  • 258.
    Chen, Shangzhi
    et al.
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kuhne, Philipp
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Knight, Sean
    Univ Nebraska, NE 68588 USA.
    Brooke, Robert
    RISE Acreo, Sweden.
    Petsagkourakis, Ioannis
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Crispin, Xavier
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Univ Nebraska, NE 68588 USA; Leibniz Inst Polymerforsch Dresden eV, Germany.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Jonsson, Magnus
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    On the anomalous optical conductivity dispersion of electrically conducting polymers: ultra-wide spectral range ellipsometry combined with a Drude-Lorentz model2019In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 15, p. 4350-4362Article in journal (Refereed)
    Abstract [en]

    Electrically conducting polymers (ECPs) are becoming increasingly important in areas such as optoelectronics, biomedical devices, and energy systems. Still, their detailed charge transport properties produce an anomalous optical conductivity dispersion that is not yet fully understood in terms of physical model equations for the broad range optical response. Several modifications to the classical Drude model have been proposed to account for a strong non-Drude behavior from terahertz (THz) to infrared (IR) ranges, typically by implementing negative amplitude oscillator functions to the model dielectric function that effectively reduce the conductivity in those ranges. Here we present an alternative description that modifies the Drude model via addition of positive-amplitude Lorentz oscillator functions. We evaluate this so-called Drude-Lorentz (DL) model based on the first ultra-wide spectral range ellipsometry study of ECPs, spanning over four orders of magnitude: from 0.41 meV in the THz range to 5.90 eV in the ultraviolet range, using thin films of poly(3,4-ethylenedioxythiophene): tosylate (PEDOT: Tos) as a model system. The model could accurately fit the experimental data in the whole ultrawide spectral range and provide the complex anisotropic optical conductivity of the material. Examining the resonance frequencies and widths of the Lorentz oscillators reveals that both spectrally narrow vibrational resonances and broader resonances due to localization processes contribute significantly to the deviation from the Drude optical conductivity dispersion. As verified by independent electrical measurements, the DL model accurately determines the electrical properties of the thin film, including DC conductivity, charge density, and (anisotropic) mobility. The ellipsometric method combined with the DL model may thereby become an effective and reliable tool in determining both optical and electrical properties of ECPs, indicating its future potential as a contact-free alternative to traditional electrical characterization.

  • 259.
    Chen, Wei Min
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nishibayashi, K.
    Kay, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Thaler, G.
    Frazier, R.
    Abernathy, C.R.
    Ren, F.
    Pearton, S.J.
    Pan, C.-C.
    Chen, G.-T.
    Chyi, J.-I.
    Zavada, J.M.
    Fast spin relaxation in InGaN/GaMnN spin LEDs: an obstacle to spin detection for future spintronics applications2005In: 3rd annual Nano Materials for Defense Applications Symposium,2005, 2005, p. 31-31Conference paper (Other academic)
    Abstract [en]

    Abstract Book of the 3rd annual Nano Materials for Defense Applications Symposium

  • 260.
    Chen, Weimin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, Department of Thematic Studies. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Extraordinary Defect-enabled Spin Functionalities in Semiconductors (invited talk)Extraordinary Defect-enabled Spin Functionalities in Semiconductors2016In: Proc. of the 33rd Int. Conf. Phys. Semicond. (2017) in press, 2016Conference paper (Refereed)
  • 261.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kayanuma, K.
    Murayama, A.
    Oka, Y.
    Toropov, A.A.
    Ivanov, S.V.
    Kop¿ev, P.S.
    Physics of optical spin injection in ZnMnSe/ZnCdSe Quantum Structures2004In: 5th International Conference on Low Dimensional Structures and Devices,2004, 2004, p. 18-Conference paper (Other academic)
  • 262.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kayanuma, K.
    Nishibayashi, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Toropov, A.A.
    Lebedev, A.V.
    Sorokin, S.V.
    Identification of a dominant mechanism for optical spin injection from a diluted magnetic semiconductor: Spin-conserving energy transfer via localized excitations2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 7, p. 73206-Article in journal (Refereed)
    Abstract [en]

    We provide compelling experimental evidence for a spin-conserving energy-transfer process via localized excitations as being responsible for the observed optical spin injection in ZnMnSe ZnCdSe quantum structures. We show that such a process is common and inherent to a diluted magnetic semiconductor because of strong potential fluctuations. © 2005 The American Physical Society.

  • 263.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Murayama, A.
    Oka, Y.
    Norton, D.P.
    Pearton, S.J.
    Osinsky, A.
    Dong, J.W.
    ZnO for spintronics: some critical issues2007In: Abstract Book of the 2007 MRS Fall Meeting, 2007, p. 326-Conference paper (Other academic)
  • 264.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Murayama, A.
    Oka, Y.
    Pearton, S.J.
    Norton, D.P.
    Abernathy, C.R.
    Osinsky, A.
    Dong, J.W.
    Spin dynamics in wide bandgap semiconductors and nanostructures - potential spintronic materials2007In: XVI International Materials Research Congress,2007, 2007Conference paper (Other academic)
    Abstract [en]

      

  • 265.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nishibayashi, K.
    Kayanuma, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Thaler, G.
    Frazier, R.
    Abernathy, C.R.
    Pearton, S.J.
    Kim, Jihyun
    Ren, F.
    Kyrychenko, F.V.
    Stanton, C.
    Pan, C.-C.
    Chen, G.T.
    Chyi, J.I.
    Zavada, J.M.
    Spin relaxation in InGaN/Ga(Mn)N quantum wells2005In: Bulletin of the American physical society, ISSN 0003-0503, Vol. 50, p. 609-609Article in journal (Refereed)
    Abstract [en]

    Proc. 2005 APS March Meeting, March 21-25, 2005; Los Angeles, CA, USA

  • 266.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nishibayashi, K.
    Kayanuma, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Thaler, G.
    Frazier, R.
    Abernathy, C.R.
    Ren, F.
    Pearton, S.J.
    Pan, C.-C.
    Chen, G.-T.
    Chyi, J.-I
    Efficient spin relaxation in InGaN/GaN and InGaN/GaMnN quantum wells: An obstacle to spin detection2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, no 19, p. 192107-Article in journal (Refereed)
    Abstract [en]

    Transient magneto-optical spectroscopy of InGaNGaN and InGaNGaMnN quantum wells reveals a spin relaxation process with a characteristic time of 50 ps. We show that the observed spin relaxation is mediated by spin flips of individual carriers rather than by direct exciton spin flips, and is proposed to occur near the bottom of the exciton band (K=0). Nearly complete thermalization between spin sublevels of the excitons, observed immediately after the pulsed photoexcitation, is attributed to even faster spin relaxation of photogenerated hot carriers/excitons accompanying momentum and energy relaxation at high K vectors. © 2005 American Institute of Physics.

  • 267.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nishibayashi, K.
    Kayanuma, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Thaler, G.
    Frazier, R.
    Abernathy, C.R.
    Ren, F.
    Pearton, S.J.
    Pan, C.C.
    Chen, G.T.
    Chyi, J.I.
    Transient Magneto-optical Spectroscopy of Spin-LED Structures2006In: 11th International Conferences on Modern Materials and Technologies,2006, 2006, p. SS2.1:P0-Conference paper (Other academic)
    Abstract [en]

      

  • 268.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Nishibayashi, K.
    Kayanuma, K.
    Seo, K.
    Murayama, A.
    Oka, Y.
    Thaler, G.
    Frazier, R.
    Abernathy, C.R.
    Ren, F.
    Pearton, S.J.
    Pan, C.-C.
    Chen, G.-T.
    Chyi, J.-I.
    Zavada, J.M.
    InGaN quantum wells for spin detection: obstacles and prospects2005In: Workshop on Semiconductor Materials for Room Temperature Spintronic Applications,2005, 2005Conference paper (Other academic)
  • 269.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan.
    Abernathy, C.R.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Prospects of potential semiconductor spin detectors2007In: Advances in Nanomaterials and Processing, Pts 1 and 2 / [ed] Byung Tae Ahn, Hyeongtag Jeon, Bo Young Hur, Kibae Kim and Jong Wan Park, Trans Tech Publications Inc., 2007, p. 839-842Conference paper (Refereed)
    Abstract [en]

    We review our recent experimental findings by optical orientation spectroscopy that show efficient spin relaxation within semiconductor spin detectors to be an important factor limiting efficiency of spin injection in spin light-emitting structures based on ZnCdSe/ZnMnSe and InGaN/GaMnN. We provide evidence for the physical mechanism responsible for the observed efficient spin relaxation that accompanies momentum and energy relaxation of excitons/carriers. These findings call for increasing efforts in suppressing spin relaxation in spin detectors.

  • 270.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Oka, Y.
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan.
    Abernathy, C.R.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Pearton, S.J.
    Department of Materials Science and Engineering, University of Florida, Gainesville, FL, USA.
    Spin depolarization in semiconductor spin detectors2006In: Proc. of SPIE Vol. 6118: Ultrafast Phenomena in Semiconductors and Nanostructure Materials X / [ed] K.-T. Tsen, J.-J. Song, H. Jiang, SPIE - International Society for Optical Engineering, 2006, p. 611804-1-611804-12Conference paper (Other academic)
    Abstract [en]

    A brief review is given of our recent experimental results from in-depth investigations of spin depolarization and underlying physical mechanisms within semiconductor spin detectors based on II-VIs (e.g. Zn(Cd)Se quantum wells) and III-Vs (e.g. InGaN quantum wells), which are relevant to applications for spin-LEDs based on ZnMnSe/Zn(Cd)Se and GaMnN/InGaN structures. By employing cw and time-resolved magneto-optical and optical spin orientation spectroscopy in combination with tunable laser excitation, we show that spin depolarization within these spin detectors is very efficient and is an important factor limiting efficiency of spin detection. Detailed physical mechanisms leading to efficient spin depolarization will be discussed.

  • 271.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Sörman, E.
    Hai, P. N.
    Wagner, Matthias
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Magneto-optical spectroscopy of defects in wide bandgap semiconductors: GaN and SiC2000In: Proceedings Conference on Optoelectronic and Microelectronic Materials and Devices, IEEE , 2000, p. 497-502Conference paper (Refereed)
    Abstract [en]

    We review recent progress in our understanding of intrinsic defects in GaN and SiC, gained from magneto-optical studies by Zeeman measurements and optically detected magnetic resonance. The two best-known intrinsic defects in these two wide bandgap semiconductors, i.e. the Ga interstitial in GaN and the silicon vacancy in SiC, are discussed in detail. The Ga interstitial is the first and only intrinsic defect in GaN that has so far been unambiguously identified, either in the presumably isolated form or in a family of up to three complexes. The silicon vacancy is among the most studied intrinsic defect in SiC, at least in two charge states, and yet still remains controversial.

  • 272.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Tu, C.W.
    Yonezu, H.
    Defects in dilute nitrides2005Conference paper (Refereed)
    Abstract [en]

    We provide a brief review of our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in dilute nitrides, i.e. Ga(In)NAs and Ga(Al,In)NP. Defect complexes involving intrinsic defects such as As-Ga antisites and Ga-i self-interstitials were positively identified. Effects of growth conditions, chemical compositions and post-growth treatments on formation of the defects are closely examined. These grown-in defects are shown to play an important role in non-radiative carrier recombination and thus in degrading optical quality of the alloys, harmful to performance of potential optoelectronic and photonic devices based on these dilute nitrides.

  • 273.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Wagner, Matthias
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lindström, J. L.
    Amano, H.
    Akasaki, I.
    Role of the Substitutional Oxygen Donor in the Residual n-type Conductivity in GaN1999Conference paper (Refereed)
    Abstract [en]

     A detailed photoluminescence (PL) study reveals a striking similarity in local vibrational properties of a defect center in GaN as compared to that for the substitutional OP donor in GaP. This observation could be interpreted as if the center is in fact related to the substitutional oxygen donor in GaN. The deep-level nature experimentally determined for the defect center calls for caution of a commonly referred model that the substitutional oxygen donor is responsible for the residual n-type conductivity in GaN.

  • 274.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Hai, P. N.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Xin, H. P.
    Tu, C. W.
    Optical Detection of Cyclotron Resonance (ODCR) in GaNAs/GaAs Quantum Well Structures2000Conference paper (Refereed)
    Abstract [en]

    ODCR has been employed to study effective masses and carrier recombination in GaNAs/GaAs multi-quantum well (MQW) structures, prepared by MBE with the nitrogen composition up to 4.5 above GaAs bandgap excitation consists of the excitonic recombination within the GaNAs MQW, the band edge PL emissions from GaAs and a broad 0.8-eV PL of unknown origin. When monitoring these emissions under the above GaAs excitation, the ODCR spectrum is dominated by the electron and hole CR in GaAs, with effective mass values 0.07m0 and 0.5m_0, respectively. The ODCR mechanism is discussed in terms of hot carrier effects, resulting in a reduced carrier recombination in GaAs and an enhanced carrier trapping in the GaNAs MQW. Under resonant excitation of the GaNAs MQW only a broad ODCR signal can be observed corresponding to an effective mass value 0.1m_0, attributed to the electron CR in the GaNAs MQW, where a higher electron effective mass value and a much lower mobility are expected.

  • 275.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Hai, P. N.
    Wagner, Matthias
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Amano, H.
    Akasaki, I.
    Xin, H. P.
    Tu, C. W.
    Optical and Microwave Double Resonance of III-nitrides1999In: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999, 1999, p. 764-Conference paper (Other academic)
    Abstract [en]

      

  • 276.
    Chen, Yen-Ting
    et al.
    Academic Sinica, Taiwan .
    Araki, Tsutomu
    Ritsumeikan University, Japan .
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Chen, Li-Chyong
    National Taiwan University, Taiwan .
    Chen, Kuei-Hsien
    Academic Sinica, Taiwan .
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nanishi, Yasushi
    Ritsumeikan University, Japan .
    Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 20, p. 203108-Article in journal (Refereed)
    Abstract [en]

    Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (andlt; 35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a "narrow-pass" approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.

  • 277.
    Chen, Yen-Ting
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Karlsson, K. Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Determination of critical diameters for intrinsic carrier diffusion-length of GaN nanorods with cryo-scanning near-field optical microscopy2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, no 21482, p. 1-7Article in journal (Refereed)
    Abstract [en]

    Direct measurements of carrier diffusion in GaN nanorods with a designed InGaN/GaN layer-in-a-wire structure by scanning near-field optical microscopy (SNOM) were performed at liquid-helium temperatures of 10 K. Without an applied voltage, intrinsic diffusion lengths of photo-excited carriers were measured as the diameters of the nanorods differ from 50 to 800 nm. The critical diameter of nanorods for carrier diffusion is concluded as 170 nm with a statistical approach. Photoluminescence spectra were acquired for different positions of the SNOM tip on the nanorod, corresponding to the origins of the well-defined luminescence peaks, each being related to recombination-centers. The phenomenon originated from surface oxide by direct comparison of two nanorods with similar diameters in a single map has been observed and investigated.

  • 278.
    Choi, J H
    et al.
    Grenoble INP MINATEC, France LTM CNRS, France .
    Latu-Romain, L
    LTM CNRS, France .
    Bano, E
    Grenoble INP MINATEC, France .
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lee, W J
    Dong Eui University, South Korea .
    Chevolleau, T
    LTM CNRS, France .
    Baron, T
    LTM CNRS, France .
    Comparative study on dry etching of alpha- and beta-SiC nano-pillars2012In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 87, p. 9-12Article in journal (Refereed)
    Abstract [en]

    Different polytypes (alpha-SiC and beta-SiC) and crystallographic orientations ((0001) and (11-20) of 6H-SiC) have been used in order to elaborate silicon carbide (SiC) nanopillars using the inductively coupled plasma etching method. The cross section of the SiC pillars shows a rhombus, pentagonal or hexagonal morphology depending on polytypes and crystallographic orientations. The favored morphologies of SiC nanopillars originate from a complex interplay between their polytypes and crystal orientations, which reflects the so-called Wulffs rule.

  • 279.
    Choubina, Tatiana
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Glasov, M.M.
    Toropov, A.A.
    Ivchenko, E.L.
    Usui, A.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Light diffusion in GaN epilayers2007In: 3rd International Conference on Spontaneous Coherence in Excitonic System,2007, 2007Conference paper (Other academic)
  • 280.
    Choubina, Tatiana
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Glazov, M.M.
    Toropov, A.A.
    Gippius, N.A.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Usui, A.
    Vasson, A.
    Leymarie, J.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kopev, P.S.
    Slow light in GaN2008In: 16th Int. Symp. ¿Nanostructures: Physics and Technology,2008, 2008, p. 257-Conference paper (Refereed)
  • 281.
    Choubina, Tatiana
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Glazov, M.M.
    Toropov, A.A.
    Gippius, N.A.
    Vasson, A.
    Leymarie, J.
    Kavokin, A.
    Usui, A.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    The slow light in GaN2008In: ICPS2008,2008, 2008, p. 647-Conference paper (Refereed)
  • 282.
    Choubina, Tatiana
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Glazov, M.M.
    Toropov, A.A.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Gippius, N.A.
    Vasson, A.
    Leymaire, J.
    Kavokin, A.
    Usui, A.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Realization of slow light in GaN crystals2008In: IWN 2008,2008, 2008Conference paper (Refereed)
  • 283.
    Christle, David J.
    et al.
    University of Chicago, IL 60637 USA; University of Calif Santa Barbara, CA 93106 USA.
    Falk, Abram L.
    University of Chicago, IL 60637 USA.
    Andrich, Paolo
    University of Chicago, IL 60637 USA; University of Calif Santa Barbara, CA 93106 USA.
    Klimov, Paul V.
    University of Chicago, IL 60637 USA; University of Calif Santa Barbara, CA 93106 USA.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Tien Son, Nguyen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ohshima, Takeshi
    Japan Atom Energy Agency, Japan.
    Awschalom, David D.
    University of Chicago, IL 60637 USA; University of Calif Santa Barbara, CA 93106 USA.
    Isolated electron spins in silicon carbide with millisecond coherence times2015In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 14, no 2, p. 160-163Article in journal (Refereed)
    Abstract [en]

    The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries(1). Nonetheless, because certain SiC defects have electronic states with sharp optical and spin transitions, they are increasingly recognized as a platform for quantum information and nanoscale sensing(2-16). Here, we show that individual electron spins in high-purity monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects(2,3), these states exhibit exceptionally long ensemble Hahn-echo spin coherence times, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route towards wafer-scale quantum technologies.

  • 284.
    Christle, David J.
    et al.
    University of Chicago, IL 60637 USA.
    Klimov, Paul V.
    University of Chicago, IL 60637 USA.
    de las Casas, Charles F.
    University of Chicago, IL 60637 USA.
    Szasz, Krisztian
    Hungarian Academic Science, Hungary.
    Ivády, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Koehl, William F.
    University of Chicago, IL 60637 USA.
    Ohshima, Takeshi
    National Institute Quantum and Radiol Science and Technology, Japan.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    Awschalom, David D.
    University of Chicago, IL 60637 USA.
    Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface2017In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 7, no 2, article id 21046Article in journal (Refereed)
    Abstract [en]

    The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects.

  • 285.
    Chua, Cassandra
    et al.
    University of Cambridge, England .
    Connolly, Malcolm
    University of Cambridge, England National Phys Lab, England .
    Lartsev, Arseniy
    Chalmers, Sweden .
    Yager, Tom
    Chalmers, Sweden .
    Lara-Avila, Samuel
    Chalmers, Sweden .
    Kubatkin, Sergey
    Chalmers, Sweden .
    Kopylov, Sergey
    University of Lancaster, England .
    Falko, Vladimir
    University of Lancaster, England .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pearce, Ruth
    National Phys Lab, England .
    Janssen, T.J. B. M.
    National Phys Lab, England .
    Tzaenchuk, Alexander
    National Phys Lab, England University of London, England .
    Smith, Charles G.
    University of Cambridge, England .
    Quantum Hall Effect and Quantum Point Contact in Bilayer-Patched Epitaxial Graphene2014In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, no 6, p. 3369-3373Article in journal (Refereed)
    Abstract [en]

    We study an epitaxial graphene monolayer with bilayer inclusions via magnetotransport measurements and scanning gate microscopy at low temperatures. We find that bilayer inclusions can be metallic or insulating depending on the initial and gated carrier density. The metallic bilayers act as equipotential shorts for edge currents, while closely spaced insulating bilayers guide the flow of electrons in the monolayer constriction, which was locally gated using a scanning gate probe.

  • 286.
    Chua, Cassandra
    et al.
    University of Cambridge, England.
    Lartsev, Arseniy
    Chalmers, Sweden.
    Sui, Jinggao
    University of Cambridge, England.
    Panchal, Vishal
    National Phys Lab, England.
    Puddy, Reuben
    University of Cambridge, England.
    Richardson, Carly
    University of Cambridge, England.
    Smith, Charles G.
    University of Cambridge, England.
    Janssen, T. J. B. M.
    National Phys Lab, England.
    Tzalenchuk, Alexander
    National Phys Lab, England; Royal Holloway University of London, England.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kubatkin, Sergey
    Chalmers, Sweden.
    Connolly, Malcolm R.
    University of Cambridge, England.
    Observation of Coulomb blockade in nanostructured epitaxial bilayer graphene on SiC2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 119, p. 426-430Article in journal (Refereed)
    Abstract [en]

    We study electron transport in nanostructures patterned in bilayer graphene patches grown epitaxially on SiC as a function of doping, magnetic field, and temperature. Away from charge neutrality transport is only weakly modulated by changes in carrier concentration induced by a local side-gate. At low n-type doping close to charge neutrality, electron transport resembles that in exfoliated graphene nanoribbons and is well described by tunnelling of single electrons through a network of Coulomb-blockaded islands. Under the influence of an external magnetic field, Coulomb blockade resonances fluctuate around an average energy and the gap shrinks as a function of magnetic field. At charge neutrality, however, conduction is less insensitive to external magnetic fields. In this regime we also observe a stronger suppression of the conductance below T*, which we interpret as a sign of broken interlayer symmetry or strong fluctuations in the edge/potential disorder. (C) 2017 Elsevier Ltd. All rights reserved.

  • 287.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Czigany, Zsolt
    Hungarian Academic Science, Hungary .
    Andersson, Sven G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Nucleation and initial growth of sp2-BNon α-Al2O3 and SiC by chemical vapour deposition2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Knowledge on thin films evolution from the early stages of growth is important for the control of quality and properties of the film. Here we present study of the early growth stages and evolution of the crystalline structure of sp2 hybridised Boron Nitride (BN) thin films deposited by chemical vapour deposition from triethyl boron and ammonia. Nucleation of hexagonal BN (h-BN) is observed already at 1200 °C on α-Al2O3 substrate with an AlN buffer layer (AlN/α-Al2O3) while no formation of h-BN is detected when the growth is done on 6H-SiC in a growth temperature range between 1200 °C and 1700 °C. We demonstrate that h-BN grows on AlN/α-Al2O3 exhibiting a layer-by-layer growth mode up to ca. 4 nm followed by a transition to r-BN growth when grown at 1500 °C. The following r-BN growth is suggested to proceed with mixed layer-by-layer and island growth mode; after a thin continuous layer of r-BN, islands formation is favoured leading to a twinned r-BN structure of the film. We find that h-BN does not grow on 6H-SiC substrates instead r-BN nucleates and grows directly as a twinned crystal. The twinning is found to be suppressed by a surface preparation of the SiC substrate with SiH4 prior to BN growth. These results open up for a more controlled epitaxial growth of sp2-BN for future electronic applications.

  • 288.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    On the effect of silicon in CVD of sp2 hybridized boron nitride thin films2013In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 3, p. 455-458Article in journal (Refereed)
    Abstract [en]

    The influence of silicon on the growth of epitaxial rhombohedral boron nitride (r-BN) films deposited on sapphire (0001) by chemical vapor deposition is investigated. X-ray diffraction measurements and secondary ion mass spectrometry show that silicon favors the formation of r-BN and is incorporated into the film.

  • 289.
    Chubarov, Mikhail
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of High Quality Epitaxial Rhombohedral Boron Nitride2012In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 12, no 6, p. 3215-3220Article in journal (Refereed)
    Abstract [en]

    Epitaxial growth of sp(2)-hybridized boron nitride (sp(2) BN) films on sapphire substrates is demonstrated in a hot wall chemical vapor deposition reactor at the temperature of 1500 degrees C, using triethyl boron and ammonia as precursors. The influence of the main important process parameters, temperature, N/B ratio, B/H-2 ratio, and carrier gas composition on the quality of the grown layers is investigated in detail. X-ray diffraction shows that epitaxial rhombohedral BN (r-BN) film can be deposited only in a narrow process parameter window; outside this window either turbostratic-BN or amorphous BN is favored if BN is formed. In addition, a thin strained AlN buffer layer is needed to support epitaxial growth of r-BN film on sapphire since only turbostratic BN is formed on sapphire substrate. The quality of the grown film is also affected by the B/H-2 ratio as seen from a change of the spacing between the basal planes as revealed by X-ray diffraction. Time-of-flight elastic recoil detection analysis shows an enhancement of the C and O impurities incorporation at lower growth temperatures. The gas phase chemistry for the deposition is discussed as well as the impact of the growth rate on the quality of the BN film.

  • 290. Chung, HJ
    et al.
    Liu, JQ
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Skowronski, M
    Stacking fault formation in highly doped 4H-SiC epilayers during annealing2003Conference paper (Refereed)
    Abstract [en]

    Spontaneous stacking fault formation during annealing in n(+) 4H-SiC epilayers deposited on the n(-) 4H-SiC substrates has been analyzed by conventional and high-resolution transmission electron microscopy (HRTEM). All faults were double layer Shockley faults formed by glide of partial dislocations on two neighboring basal planes. Ends of stacking faults were examined with high-resolution TEM. Approximately half of bounding partial dislocations had extra half planes extending into the substrate while the other half had half planes pointing toward epilayer. This observation is inconsistent with mechanical stress due to doping difference between epilayer and the substrate being the driving force of fault expansion. Formation of single Shockley stacking faults was also observed in n(+) 6H-SiC.

  • 291.
    Ciechonski, Rafal
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Device characteristics of sublimation grown 4H-SiC layers2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the licentiate thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. We have identified a carbonization of the source as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized.

    The major focus of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and the purity of grown layers.

    High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 Ωcm. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DL TS data is taken into account to support the model.

    To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects.

    On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T-1.3 and T-2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism.

    Metal-Oxide-Semiconductor (MOS) capacitors were fabricated and characterized on 4H-SiC epilayers grown by PVT (sublimation) epitaxy and compared to the properties of similar structures on CVD grown layers. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from roomtemperature up to 475 K. The amount of positive oxide charges Qo is 6.83x109 cm-2 at room temperature and decreases with temperature increase which suggests temperature stability of processed devices. The density of interface states Dit obtained by AC conductance method is lower in the case of PVT sample.

    AI203 as an alternative gate dielectric was studied. The implementation of this high-k dielectric is required in the case of high electric fields at which the usage of SiO2 may result in the reliability problems. The electrical properties of AI2O3 as a gate dielectric in MOS structures based on n- and p-type 4H-SiC grown by sublimation method were investigated and compared to the properties of similar structures utilizing SiO2.

    List of papers
    1. Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    Open this publication in new window or tab >>Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    2003 (English)In: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, p. 75-78Conference paper, Published paper (Refereed)
    Abstract [en]

    Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

    Keywords
    Bulk Growth, Doping, Boron, Tantalum, Cathodoluminescence
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12782 (URN)10.4028/www.scientific.net/MSF.433-436.75 (DOI)
    Conference
    ECSCRM 2002. Linköping, Sweden, September 1-5, 2002
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    2. Structural instabilities in growth of SiC crystals
    Open this publication in new window or tab >>Structural instabilities in growth of SiC crystals
    2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, no 1-2, p. e461-e466Article in journal (Refereed) Published
    Abstract [en]

    Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

    Keywords
    Crystal morphology; Volume defects; Growth from vapor; Single crystal growth; Semiconductor silicon compounds
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-12783 (URN)10.1016/j.jcrysgro.2004.11.020 (DOI)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    3. Growth of device quality 4H-SiC by high velocity epitaxy
    Open this publication in new window or tab >>Growth of device quality 4H-SiC by high velocity epitaxy
    2004 (English)In: Materials Science Forum, Vols. 457-460, 2004, Vol. 457-460, p. 201-204Conference paper, Published paper (Refereed)
    Abstract [en]

    Thick (>20 μm) 4H-SiC layers in doping range of low 1015-1016 cm-3 were grown by sublimation epitaxy at a growth rate of similar to50 mum/hour. Two inch 25 μm thick layers were fabricated with standard thickness deviation of 3.77%. Effect of important process parameters on the material grade has been discussed. The Schottky diodes processed on this material sustained 900V reverse voltage at a current of 1.7 x 10-8 A, while measured on MOS capacitors the interface state density was as low as similar to6-9 x 1010 cm-2.

    Keywords
    fast growth, sublimation epitaxy, 4H-SiC, device quality, schottky diode, MOS capacitor, interface state density
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-48297 (URN)10.4028/www.scientific.net/MSF.457-460.201 (DOI)
    Conference
    ICSCRM 2003, Lyon, Fance, October 5-10, 2003
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2013-11-07
    4. Effect of boron on the resistivity of compensated 4H-SiC
    Open this publication in new window or tab >>Effect of boron on the resistivity of compensated 4H-SiC
    2003 (English)In: Journal of electronic materials, ISSN 0361-5235, Vol. 32, no 5, p. 452-457Article in journal (Refereed) Published
    Abstract [en]

    High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

    Keywords
    SiC sublimation epitaxy, DLTS, compensation, deep levels, carbon vacancy, high resistivity, semi-insulating
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12784 (URN)10.1007/s11664-003-0177-0 (DOI)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    5. Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    Open this publication in new window or tab >>Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    2005 (English)In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, p. 425-428Conference paper, Published paper (Refereed)
    Abstract [en]

    Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

    Keywords
    On-state resistance, I-V, C-V, MCTS, Sublimation, High-speed epitaxy, Deep
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12785 (URN)
    Conference
    ECSCRM2004
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    6. Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    Open this publication in new window or tab >>Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    2005 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, no 13, p. 2508-2514Article in journal (Refereed) Published
    Abstract [en]

    This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2005
    Keywords
    73.20.Hb, 73.30.+y, 73.40.Ns, 73.61.Le
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-12786 (URN)10.1002/pssa.200521147 (DOI)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2017-05-11Bibliographically approved
    7. Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy
    Open this publication in new window or tab >>Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy
    2005 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, no 12, p. 1917-1920Article in journal (Refereed) Published
    Abstract [en]

    MOS capacitors have been fabricated on 4H–SiC epilayers grown by physical vapor transport (PVT) epitaxy. The properties were compared with those on similar structures based on chemical vapor deposition (CVD) layers. Capacitance–voltage (CV) and conductance measurements (GV) were performed in the frequency range of 1 kHz to 1 MHz and also at temperatures up to 475 K. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from room temperature up to 475 K. The amount of positive oxide charge QO is 6.83 × 109 cm−2 at room temperature and decreases with temperature increase. This suggests that the processed devices are temperature stable. The density of interface states Dit obtained by Nicollian–Brews conductance method is lower in the structure based on the PVT grown sample.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-30706 (URN)10.1016/j.sse.2005.08.008 (DOI)16318 (Local ID)16318 (Archive number)16318 (OAI)
    Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
    8. Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
    Open this publication in new window or tab >>Electrical behavior of 4H-SiC metal-oxide-semiconductor structures with Al2O3 as gate dielectric
    Show others...
    2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 12, p. 124507-Article in journal (Refereed) Published
    Abstract [en]

    The electrical properties of Al2O3 as a gate dielectric in metal-oxide-semiconductorstructures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by capacitance–voltage (C–V) and current–voltage (I–V) methods. The results show that the type as well as spatial and energy distributions of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better electrical characteristics than the p-type 4H-SiC/SiO2 structures. It is demonstrated that the conduction process in the former is governed by Fowler–Nordheim electron tunneling from the Al gate whereas in the latter the hole tunneling from SiC is the more probable process. This difference combined with the higher defect density in p-type SiC/SiO2 structures defines the higher leakage currents compared to the structures utilizing Al2O3.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-30684 (URN)10.1063/1.1938267 (DOI)16289 (Local ID)16289 (Archive number)16289 (OAI)
    Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
  • 292.
    Ciechonski, Rafal
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Growth and characterization of SiC and GaN2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. Carbonization of the source was identified as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized.

    The focus of the SiC part of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and purity of grown layers.

    High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 cm. By correlation between the growth conditions and SIMS results, a model was applied in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

    To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects.

    On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy (MCTS), an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism.

    In the second part of the thesis growth and characterization of GaN is presented. Excellent electron transport properties with high electron saturate drift velocity make GaN an excellent candidate for electronic devices. Especially, AlGaN/GaN based high electron mobility transistors (HEMT) have received an increased attention in last years due to their attractive properties. The presence of strong spontaneous and piezoelectric polarization due to the lattice mismatch between AlGaN and GaN is responsible for high free electrons concentrations present in the vicinity of the interface. Due to the spatial separation of electrons and ionized donors or surface states, 2DEG electron gas formed near the interface of the heterostructure exhibits high sheet carrier density and high mobility of electrons. Al0.23Ga0.77N/GaN based HEMT structures with an AlN exclusion layer on 100 mm semiinsulating 4H-SiC substrates have been grown by hot-wall MOCVD. The electrical properties of the two-dimensional electron gas (2DEG) such as electron mobility, sheet carrier density and sheet resistance were obtained from Hall measurements, capacitance-voltage and contact-less eddy-current techniques. The effect of different scattering mechanisms on the mobility have been taken into account and compared to the experimental data. Hall measurements were performed in the range of 80 to 600 K. Hall electron mobility is equal to 17140 cm2(Vs)-1 at 80 K, 2310 cm2(Vs)-1 at room temperature, and as high as 800 cm2(Vs)-1 at 450 K, while the sheet carrier density is 1.04x1013 cm-2 at room temperature and does not vary very much with temperature. Estimation of different electron scattering mechanisms reveals that at temperatures higher than room temperature, experimental mobility data is mainly limited by optical phonon scattering. At relevant high power device temperature (450 K) there is still an increase of mobility due to the AlN exclusion layer.

    We have studied the behaviour of Ga-face GaN epilayers after in-situ thermal treatment in different gas mixtures in a hot-wall MOCVD reactor. Influence of N2, N2+NH3 and N2+NH3+H2 ambient on the morphology was investigated in this work. The most stable thermal treatment conditions were obtained in the case of N2+NH3 gas ambients. We have also studied the effect of the increased molar ratio of hydrogen in order to establish proper etching conditions for hot-wall MOCVD growth.

    List of papers
    1. Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    Open this publication in new window or tab >>Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation
    2003 (English)In: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, p. 75-78Conference paper, Published paper (Refereed)
    Abstract [en]

    Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

    Keywords
    Bulk Growth, Doping, Boron, Tantalum, Cathodoluminescence
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12782 (URN)10.4028/www.scientific.net/MSF.433-436.75 (DOI)
    Conference
    ECSCRM 2002. Linköping, Sweden, September 1-5, 2002
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    2. Structural instabilities in growth of SiC crystals
    Open this publication in new window or tab >>Structural instabilities in growth of SiC crystals
    2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, no 1-2, p. e461-e466Article in journal (Refereed) Published
    Abstract [en]

    Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

    Keywords
    Crystal morphology; Volume defects; Growth from vapor; Single crystal growth; Semiconductor silicon compounds
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-12783 (URN)10.1016/j.jcrysgro.2004.11.020 (DOI)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    3. Effect of boron on the resistivity of compensated 4H-SiC
    Open this publication in new window or tab >>Effect of boron on the resistivity of compensated 4H-SiC
    2003 (English)In: Journal of electronic materials, ISSN 0361-5235, Vol. 32, no 5, p. 452-457Article in journal (Refereed) Published
    Abstract [en]

    High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

    Keywords
    SiC sublimation epitaxy, DLTS, compensation, deep levels, carbon vacancy, high resistivity, semi-insulating
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12784 (URN)10.1007/s11664-003-0177-0 (DOI)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    4. Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    Open this publication in new window or tab >>Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC
    2005 (English)In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, p. 425-428Conference paper, Published paper (Refereed)
    Abstract [en]

    Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

    Keywords
    On-state resistance, I-V, C-V, MCTS, Sublimation, High-speed epitaxy, Deep
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12785 (URN)
    Conference
    ECSCRM2004
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2013-11-07
    5. Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    Open this publication in new window or tab >>Electrical Analysis and Interface States Evaluation of of Ni Schottky diodes on 4H-SiC thick epilayers
    2005 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 202, no 13, p. 2508-2514Article in journal (Refereed) Published
    Abstract [en]

    This work has been focused on characterization of thick 4H-SiC layers produced by sublimation epitaxy. Nickel Schottky contacts have been fabricated in order to characterize the grown material and evaluate the interfacial layer between metal and semiconductor. The characterization study includes current-voltage and capacitance-voltage high temperature measurements, from which Schottky barrier, net donor concentration and on-state resistance values have been extracted. The diodes show a typical behavior of J-V and C-V curves with temperature, with Schottky barrier heights of 1.3 eV ÷ 1.4 eV and net donor concentration of 4 × 1015 cm-3 ÷ 1 × 1016 cm-3. From the Bardeen's model on reverse J-V, the density of states of the interfacial layer has been estimated to 7 × 1011 eV-1 cm-2 ÷ 8 × 1011 eV-1 cm-2, a value that is similar to the density of states of oxide layers in deliberated MOS structures realized on the same epilayers.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2005
    Keywords
    73.20.Hb, 73.30.+y, 73.40.Ns, 73.61.Le
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-12786 (URN)10.1002/pssa.200521147 (DOI)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2017-05-11Bibliographically approved
    6. High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD
    Open this publication in new window or tab >>High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD
    Show others...
    2007 (English)In: Journal of Applied PhysicsArticle in journal (Refereed) Submitted
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-12787 (URN)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2015-03-11
    7. In-situ treatment of GaN epilayers in hot-wall MOCVD
    Open this publication in new window or tab >>In-situ treatment of GaN epilayers in hot-wall MOCVD
    Show others...
    (English)Manuscript (Other academic)
    Identifiers
    urn:nbn:se:liu:diva-12788 (URN)
    Available from: 2007-12-04 Created: 2007-12-04 Last updated: 2015-03-11
  • 293.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pedersen, Henrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Lundskog, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    In-situ treatment of GaN epilayers in hot-wall MOCVDManuscript (Other academic)
  • 294.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lundskog, Anders
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    High 2DEG mobility of HEMT structures grown on 100 mm SI 4H-SiC substrates by hot-wall MOCVD2007In: Journal of Applied PhysicsArticle in journal (Refereed)
  • 295.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Effect of boron on the resistivity of compensated 4H-SiC2003In: Journal of electronic materials, ISSN 0361-5235, Vol. 32, no 5, p. 452-457Article in journal (Refereed)
    Abstract [en]

    High-resistivity 4H-SiC samples grown by sublimation with a high growth rate are studied. The measurements show resistivity values up to a high of 104 Ωcm. The secondary ion mass spectroscopy (SIMS) results revealed a presence of only common trace impurities such as nitrogen, aluminum, and boron. To understand the compensation mechanism in these samples, capacitance deep-level transient spectroscopy (DLTS) on the p-type epilayers has been performed. By correlation between the growth conditions and SIMS results, we apply a model in which it is proposed that an isolated carbon vacancy donorlike level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model.

  • 296.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Porro, Samuele
    Polytechnic of Turin, Physics Department, Torino, Italy.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Evaluation of On-state Resistance and Boron-related Levels in n-type 4H-SiC2005In: Materials Science Forum, Vols. 483-485, 2005, Vol. 483-485, p. 425-428Conference paper (Refereed)
    Abstract [en]

    Specific on-resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with a literature reported values. Decrease in mobility with the temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples respectively were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy, an influence of shallow boron related levels and D-center on dependence of on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism thus resulting in high Ron.

  • 297.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Structural instabilities in growth of SiC crystals2005In: Journal of Crystal Growth, ISSN 0022-0248, Vol. 275, no 1-2, p. e461-e466Article in journal (Refereed)
    Abstract [en]

    Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.

  • 298.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Evaluation of MOS structures processed on 4H–SiC layers grown by PVT epitaxy2005In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, no 12, p. 1917-1920Article in journal (Refereed)
    Abstract [en]

    MOS capacitors have been fabricated on 4H–SiC epilayers grown by physical vapor transport (PVT) epitaxy. The properties were compared with those on similar structures based on chemical vapor deposition (CVD) layers. Capacitance–voltage (CV) and conductance measurements (GV) were performed in the frequency range of 1 kHz to 1 MHz and also at temperatures up to 475 K. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from room temperature up to 475 K. The amount of positive oxide charge QO is 6.83 × 109 cm−2 at room temperature and decreases with temperature increase. This suggests that the processed devices are temperature stable. The density of interface states Dit obtained by Nicollian–Brews conductance method is lower in the structure based on the PVT grown sample.

  • 299.
    Ciechonski, Rafal
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Effect of Ambient on 4H-SiC Bulk Crystals grown by Sublimation2003In: Materials Science Forum, Vols. 433-436 / [ed] Peder Bergman and Erik Janzén, 2003, Vol. 433-436, p. 75-78Conference paper (Refereed)
    Abstract [en]

    Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcallmole for growth temperatures below 2075°C and 128 kcal/mole in the range of growth temperatures between 2075°C and 2275°C. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-alurninum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.

  • 300.
    Civrac, Gabriel
    et al.
    University of Lyon, France .
    Laariedh, Farah
    University of Lyon, France .
    Thierry-jebali, Nicolas
    University of Lyon, France .
    Lazar, Mihai
    University of Lyon, France .
    Planson, Dominique
    University of Lyon, France .
    Brosselard, Pierre
    University of Lyon, France .
    ul Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Vergne, Bertrand
    French-German Research Institute of Saint-Louis (ISL), France.
    Scharnholz, Sigo
    German Research Institute of Saint-Louis (ISL), France.
    600 V PiN diodes fabricated using on-axis 4H silicon carbide2012In: Materials Science Forum Vol 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, p. 969-972Conference paper (Refereed)
    Abstract [en]

    This paper reports the fabrication and electrical characterization of PiN diodes on an on-axis grown epitaxial layer. TCAD simulations have been performed in order to design their architecture. Some of these diodes have a breakdown voltage around 600 V. A comparison is made with similar diodes fabricated on off-cut grown layers. Computer simulations are used to explain lower breakdown voltages than those expected.

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