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  • 1.
    Bergsten, Johan
    et al.
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gustafsson, Sebastian
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Thorsell, Mattias
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rorsman, Niklas
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Impact of AlGaN/GaN interface sharpness on HEMT performanceManuscript (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.

  • 2.
    Bergsten, Johan
    et al.
    Chalmers, Sweden.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gustafsson, Sebastian
    Chalmers, Sweden.
    Malmros, Anna
    Chalmers, Sweden.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Thorsell, Mattias
    Chalmers, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rorsman, Niklas
    Chalmers, Sweden.
    Performance Enhancement of Microwave GaN HEMTs Without an AlN-Exclusion Layer Using an Optimized AlGaN/GaN Interface Growth Process2016In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 63, no 1, p. 333-338Article in journal (Refereed)
    Abstract [en]

    The impact of the sharpness of the AlGaN/GaN interface in high-electron mobility transistors (HEMTs) is investigated. Two structures, one with an optimized AlGaN/GaN interface and another with an unoptimized, were grown using hot-wall metal-organic chemical vapor deposition. The structure with optimized sharpness of the interface shows electron mobility of 1760 cm(2)/V . s as compared with 1660 cm(2)/V . s for the nonoptimized interface. Gated Hall measurements indicate that the sharper interface maintains higher mobility when the electrons are close to the interface compared with the nonoptimized structure, indicating less scattering due to alloy disorder and interface roughness. HEMTs were processed and evaluated. The higher mobility manifests as lower parasitic resistance yielding a better dc and high-frequency performance. A small-signal equivalent model is extracted. The results indicate a lower electron penetration into the buffer in the optimized sample. Pulsed-IV measurements imply that the sharper interface provides less dispersive effects at large drain biases. We speculate that the mobility enhancement seen AlGaN/AlN/GaN structures compared with the AlGaN/GaN case is not only related to the larger conduction band offset but also due to a more welldefined interface minimizing scattering due to alloy disorder and interface roughness.

  • 3.
    Bergsten, Johan
    et al.
    Chalmers, Gothenburg, Sweden.
    Li, Xun
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Rorsman, Niklas
    Chalmers, Gothenburg, Sweden.
    AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor2016In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 55, p. 05FK02-1-05FK02-4, article id 05FK02Article in journal (Refereed)
    Abstract [en]

    AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using analternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuningthe growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growthconditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation anddispersion. Good isolation with OFF-state currents of 2 ' 10%6A/mm, breakdown fields of 70V/μm, and low drain induced barrier lowering of0.13mV/V are found. Dispersive effects are examined using pulsed current–voltage measurements. Current collapse and knee walkout effectslimit the maximum output power to 1.3W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer aversatile approach to decrease dispersive effects in GaN HEMTs.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    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.

  • 9.
    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)
  • 10.
    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)
  • 11.
    Danielsson, E.
    et al.
    KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Zetterling, C.-M.
    KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Domeij, M.
    KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Ostling, M.
    Östling, M., KTH, Dept. Microelectron./Info. Technol., P.O. Box Electrum 229, S-164 40 Kista, Sweden.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Investigation of thermal properties in fabricated 4H-SiC high power bipolar transistors2003In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 47, no 4, p. 639-644Article in journal (Refereed)
    Abstract [en]

    Silicon carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of 450 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 °C, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. The device was also tested in a switched setup, showing fast turn on and turn off at 1 MHz and 300 V supply voltage. Device simulations have been used to analyze the measured data. The thermal conductivity is fitted against the self-heating, and the lifetime in the base is fitted against the measurement of the current gain. © 2003 Elsevier Science Ltd. All rights reserved.

  • 12.
    Danielsson, E.
    et al.
    KTH.
    Zetterling, C.M.
    KTH.
    Domeij, M.
    KTH.
    Östling, M.
    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.
    Switching Peformance for Fabricated and Simulated 4H-SiC High Power Bipolar Transistors2003In: Solid State Electronics, Vol. 47, 2003, p. 639-Conference paper (Refereed)
  • 13. Danielsson, E
    et al.
    Zetterling, CM
    KTH, Dept Microelect & Informat Technol, SE-16440 Kista, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Ostling, M
    KTH, Dept Microelect & Informat Technol, SE-16440 Kista, Sweden Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden.
    Forsberg, Urban
    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.
    Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1337-1340Conference paper (Refereed)
    Abstract [en]

    Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.

  • 14.
    Danielsson, Olof
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Neuroscience and Locomotion.
    Forsberg, Urban
    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.
    Predictions of nitrogen doping in SiC epitaxial layers2003In: Materials Science Forum, Vols. 433-436, 2003, Vol. 433-4, p. 137-140Conference paper (Refereed)
    Abstract [en]

    Growth of device quality epitaxial layers requires precise control of thickness and doping uniformities. Computer simulations can provide growers with the necessary knowledge for improving and optimizing the growth process. In this work, the CVD process is simulated in three dimensions, using a reaction-mass transport model. A simplified quantitative model for the nitrogen incorporation in intentionally doped 4H-SiC samples has been developed and applied to a wide range of process parameters. Different reaction schemes are necessary for the two faces of SiC to account for the different doping incorporation behavior. The simulations are validated by experimental data measured by SIMS with good agreement.

  • 15. Danielsson, Ö
    et al.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Henry, Anne
    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.
    Enlarging the usable growth area in a hot-wall silicon carbide CVD reader by using simulation2001In: Materials Science Forum, Vols. 353-356, 2001, Vol. 353-3, p. 99-102Conference paper (Refereed)
    Abstract [en]

    The chemical vapor deposition (CVD) growth of large area silicon car-bide epitaxial layers with homogeneous properties requires a large area with homogeneous temperature in the CVD reactor. In the present work we show that by changing the design of the CVD reactor, but keeping the overall dimension the same, this area can be enlarged by at least a factor of three.. By using a simulation tool new designs can be tried out and optimized in the computer before testing them in practice. The simulation is set up as a 2D axisymmetric problem and validation is made in a 2D horizontal hot-wall CVD reactor. Very good agreements between simulated and measured results are obtained. The zone with a temperature variation of less than 5 degrees at an operating temperature of 1650 degreesC increased to 64% of the whale susceptor length. In addition, the power input needed to reach the operating temperature decreased by 15%.

  • 16.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Henry , Anne
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 235, no 1-4, p. 352-364Article in journal (Refereed)
    Abstract [en]

    The chemical vapor deposition (CVD) technique is widely used to grow epitaxial layers of silicon carbide. To meet the demands for high quality epitaxial layers, which have good morphology and a minimum variation of the doping and thickness, a good knowledge of the CVD process is essential. The present work uses a simulation tool to investigate several parameters influencing the heating of <!--[if !vml]--><!--[endif]-->a hot-wall CVD reactor. The simulations are set up as 2D axisymmetric problems and validation is made in a 2D horizontal hot-wall CVD reactor. By applying the knowledge achieved from the simulations, the temperature profile is optimized to give as large area as possible with homogeneous temperature. New susceptor and coil designs are tested. A very good agreement between the simulated and the measured results is obtained. The new design has a temperature variation of less than 0.5% over more than 70% of the total susceptor length at an operating temperature of 1650°C. In addition, the power input needed to reach the operating temperature is decreased by 15% compared to the original design. 3D simulations are performed to show that the changes made in the 2D case give similar results for the real 3D case.

  • 17.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition2003In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 250, no 3-4, p. 471-478Article in journal (Refereed)
    Abstract [en]

    A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H-SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.

  • 18.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Li, Xun
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    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, Chemistry. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    A model for carbon incorporation from trimethyl gallium in chemical vapor deposition of gallium nitride2016In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 4, no 4, p. 863-871Article in journal (Refereed)
    Abstract [en]

    Gallium nitride (GaN) semiconductor material can become semi-insulating when doping with carbon. Semi-insulating buffer layers are utilized to prevent leakage currents in GaN high power devices. Carbon is inherently present during chemical vapor deposition (CVD) of GaN from the use of trimethyl gallium (TMGa) as precursor. TMGa decomposes in the gas phase, releasing its methyl groups, which could act as carbon source for doping. It is previously known that the carbon doping levels can be controlled by tuning the CVD process parameters, such as temperature, pressure and precursor flow rates. However, the mechanism for carbon incorporation from TMGa is not yet understood. In this paper, a model for predicting carbon incorporation from TMGa in GaN layers grown by CVD is proposed. The model is based on ab initio quantum chemical calculations of molecular adsorption and reaction energies. Using Computational Fluid Dynamics, with a chemical kinetic model for decomposition of the precursors and reactions in the gas phase, to calculate gas phase compositions at realistic process conditions, together with the proposed model, we obtain good correlations with measurements, for both carbon doping concentrations and growth rates, when varying the inlet NH3/TMGa ratio. When varying temperature (800 – 1050°C), the model overpredicts carbon doping concentrations at the lower temperatures, but predicts growth rates well, and the agreement with measured carbon doping concentrations is good above 1000°C.

  • 19.
    Fagerlind, M.
    et al.
    Chalmers.
    Allerstam, F.
    Chalmers.
    Sveinbjornsson, E.O.
    Chalmers.
    Rorsman, N.
    Chalmers.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    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.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Investigation of the interface between silicon nitride passivations and AlGaN/AlN/GaN heterostructures by C(V) characterization of metal-insulator-semiconductor-heterostructure capacitors2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 1, p. 014508-Article in journal (Refereed)
    Abstract [en]

    Capacitance-voltage [C(V)] measurements of metal-insulator-semiconductor-heterostructure capacitors are used to investigate the interface between silicon nitride passivation and AlGaN/AlN/GaN heterostructure material. AlGaN/AlN/GaN samples having different silicon nitride passivating layers, deposited using three different deposition techniques, are evaluated. Different interface state distributions result in large differences in the C(V) characteristics. A method to extract fixed charge as well as traps from the C(V) characteristics is presented. Rough estimates of the emission time constants of the traps can be extracted by careful analysis of the C(V) characteristics. The fixed charge is positive for all samples, with a density varying between 1.3 x 10(12) and 7.1 x 10(12) cm(-2). For the traps, the peak density of interface states is varying between 16 x 10(12) and 31 x 10(12) cm(-2) eV(-1) for the three samples. It is concluded that, of the deposition methods investigated in this report, the low pressure chemical vapor deposited silicon nitride passivation shows the most promising results with regards to low densities of interface states.

  • 20.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    CVD Growth of Silicon Carbide for High Frequency Applications2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Silicon Carbide (SiC) is an important wide band gap semiconductor with outstanding electronic properties. With figures of merit far better than silicon, SiC is believed to replace and outcompete silicon in many applications using high frequencies, high voltage and high temperatures. With the introduction of seeded sublimation technique, a realisation of substrates with large diameter and high quality became possible. Recent progress in the bulk growth using high temperature chemical vapour deposition (HTCVD) has shown excellent results with high purity substrates with semi insulating (SI) properties. The availability of high quality SI substrates allows the fabrication of microwave devices with low rf losses such as the Metal Schottky Field Effect Transistor (MESFET). With the introduction of the hot-wall CVD technique, thick low doped n-type epitaxial layers have been grown for high power devices (> 4 kV) such as the PiN diode.

    The main contribution of the present work relates to the investigation of growth of MESFET structures. The goal has been to demonstrate the ability to grow MESFET structures using the hot-wall CVD technique. The challenge with abrupt interfaces and controlled doping has been investigated. A comprehensive investigation has been made on how nitrogen and aluminum dopant atoms incorporate into the SiC lattice using the hot-wall CVD technique. Fundamental research of MESFET structures has been combined with growth of device structures for both Swedish and European groups as well as industries. The research has been focused towards the understanding of dopant incorporation, characterization of doped epitaxial layers, the growth of device structures, the modelling of temperature distribution in a hot-wall susceptor and the development of growth systems for future up scaling.

    In paper 1 we present how the nitrogen dopant is incorporated into the SiC lattice. The influence of several different growth parameters on the nitrogen incorporation is presented. Equilibrium thermodynamical calculations have been performed to give a further insight into the incorporation mechanism. The investigation shows that the N2 molecule itself does not contribute directly to the nitrogen incorporation, however, molecules like the HCN and HNC are more likely.

    In paper 2 the incorporation of the aluminum dopant into the SiC lattice is investigated in a similar way as the nitrogen incorporation in paper 1. The results show that the aluminum incorporation in SiC is mainly controlled by the carbon coverage on the SiC surface. The investigation shows that it is difficult to obtain high aluminum doping on carbon face whereas the silicon face is sensitive to changes of the growth parameters. High growth rate resulted in a diffusion controlled incorporation.

    In Paper 3 we present the results from the growth of MESFET structures as well as characterization of the structures and final device properties. Knowledge taken from paper 1 and 2 was used to improve the abruptness of the grown structures.

    Paper 4 presents the results obtained by low temperature photoluminescence (LTPL) on separately grown 4H-SiC epitaxial layers. Doping calibration curves for nitrogen in the doping range from 1⋅1014 to 2⋅1019 cm-3 are presented. A discussion concerning the Mott transition is also presented.

    Paper 5 presents the results of the use of simulation to investigate the heating of a hot-wall CVD reactor. New susceptor and coil design are tested. The simulation has been verified with experimental heating tests which show excellent agreement. The new design has a temperature variation of less than 0.5 % over more than 70% of the total susceptor length in addition to a decreased power input of 15 %.

    In the final two papers, paper 6 and 7, we present work of growth of AlN on SiC. Thin films were grown and characterized with different techniques concerning crystal quality and thickness. The use of infrared reflectance and the features of the AlN reststrahl reflectance band allowed us to determine the thickness of AlN films as thin as 250 Å.

    List of papers
    1. Nitrogen doping of epitaxial Silicon Carbide
    Open this publication in new window or tab >>Nitrogen doping of epitaxial Silicon Carbide
    Show others...
    2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 236, no 1-3, p. 101-112Article in journal (Refereed) Published
    Abstract [en]

    Intentional doping with nitrogen of 4H- and 6H-SiC has been performed using a hot-wall CVD reactor. The nitrogen doping dependence on the temperature, pressure, C/Si ratio, growth rate and nitrogen flow has been investigated. The nitrogen incorporation for C-face material showed to be C/Si ratio independent, whereas the doping decreased with increasing C/Si ratio for the Si-face material in accordance with the “site-competition” model. The nitrogen incorporation was constant in a temperature “window” of 75°C on Si-face material indicating a mass transport limited incorporation. Increasing the growth rate resulted in a decrease of nitrogen incorporation on Si-face but an increase on C-face material. Finally, a comparison between previously published results on cold-wall CVD-grown material and the present hot-wall-grown material is presented.

    Place, publisher, year, edition, pages
    ScienceDirect, 2002
    Keywords
    A1. Doping, A3. Hot wall epitaxy, B2. Superconducting materials
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15068 (URN)10.1016/S0022-0248(01)02198-4 (DOI)
    Note
    The status of this article on the day of the defence was: Submitted and the title of the article was "Nitrogen doping of Silicon Carbide: Effect of Process Parameters"Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
    2. Aluminum doping of epitaxial Silicon Carbide
    Open this publication in new window or tab >>Aluminum doping of epitaxial Silicon Carbide
    Show others...
    2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, p. 340-350Article in journal (Refereed) Published
    Abstract [en]

    Intentional doping of aluminum in 4H and 6H SiC has been performed using a hot-wall CVD reactor. The dependence of aluminum incorporation on temperature, pressure, C/Si ratio, growth rate, and TMA flow has been investigated. The aluminum incorporation showed to be polarity dependent. The high aluminum incorporation on the Si-face is closely related to the carbon coverage on the SiC surface. Changes in process parameters changes the effective C/Si ratio close to the SiC surface. Increased growth rate and C/Si ratio increases the aluminum incorporation on the Si-face. Diffusion limited incorporation occurs at high growth rate. Reduced pressure increases the effective C/Si ratio, and at low growth rate, the aluminum incorporation increases initially, levels off at a critical pressure, and continues to decrease below the critical pressure. The aluminum incorporation showed to be constant in a temperature range of 50°C. The highest atomic concentration of aluminum observed in this study was 3×1017 and 8×1018 cm−3 in Si and C-face, respectively.

    Place, publisher, year, edition, pages
    ScienceDirect, 2003
    Keywords
    A1. Doping; A1. Growth models; A3. Chemical vapor deposition processes; A3. Hot wall epitaxy; B2. Semiconducting silicon carbide
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15055 (URN)10.1016/S0022-0248(03)01045-5 (DOI)
    Note
    The status of the article on the defence day was: Submitted and the original title was "Aluminum doping of Silicon Carbide: Effect of Process Parameters".Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
    3. Growth and characterisation 4H-SiC MESFET structures grown by Hot-Wall CVD
    Open this publication in new window or tab >>Growth and characterisation 4H-SiC MESFET structures grown by Hot-Wall CVD
    Show others...
    2001 (English)In: Proc. of the MRS 2000 Fall Meeting, 2001, p. H2.3.2-Conference paper, Published paper (Refereed)
    Abstract [en]

    Metal semiconductor field effect transistor structures have been grown in a hot-wall CVD reactor. Using trimethylaluminium and nitrogen, p- and n-type epitaxial layers were grown on semi insulating substrates. A comprehensive characterization study of thickness and doping of these multi structures has been performed by using scanning electron microscopy , secondary ion mass spectrometry, capacitance-voltage and low temperature photoluminescence. Optimisation of growth parameters has resulted in very abrupt doping profiles. The grown metal semiconductor field effect transistor structures have been processed and parts of the transistor properties are presented.

    Keywords
    Hot-Wall CVD, MESFET, Silicon carbide, SEM, SIMS
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15062 (URN)
    Conference
    MRS 2000 Fall Meeting
    Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2016-08-31Bibliographically approved
    4. Determination of nitrogen doping concentration in doped 4H-SiC epilayers by low temperature photoluminescence
    Open this publication in new window or tab >>Determination of nitrogen doping concentration in doped 4H-SiC epilayers by low temperature photoluminescence
    2005 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, no 2-3, p. 254-257Article in journal (Refereed) Published
    Abstract [en]

    A complete calibration of nitrogen concentration in doped 4H-SiC material is presented. This is done in the very large range of doping available today, i.e. from low 1014 to 1019 cm-3. The samples are 4H-SiC films fabricated by hot-wall chemical vapour deposition. Low temperature photoluminescence is used as the experimental tool. For doping concentrations less than 8 × 1017 cm-3 comparison between the intensity of various luminescence lines is used, whereas for doping higher than 3 × 1018 cm-3 the energy position of an observed broad band allows the determination of the doping level.

    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15063 (URN)10.1238/Physica.Regular.072a00254 (DOI)
    Note
    On the day of the defence the status of article IV was: Submitted to Applied Physics Letter.Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
    5. Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor
    Open this publication in new window or tab >>Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor
    2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 235, no 1-4, p. 352-364Article in journal (Refereed) Published
    Abstract [en]

    The chemical vapor deposition (CVD) technique is widely used to grow epitaxial layers of silicon carbide. To meet the demands for high quality epitaxial layers, which have good morphology and a minimum variation of the doping and thickness, a good knowledge of the CVD process is essential. The present work uses a simulation tool to investigate several parameters influencing the heating of <!--[if !vml]--><!--[endif]-->a hot-wall CVD reactor. The simulations are set up as 2D axisymmetric problems and validation is made in a 2D horizontal hot-wall CVD reactor. By applying the knowledge achieved from the simulations, the temperature profile is optimized to give as large area as possible with homogeneous temperature. New susceptor and coil designs are tested. A very good agreement between the simulated and the measured results is obtained. The new design has a temperature variation of less than 0.5% over more than 70% of the total susceptor length at an operating temperature of 1650°C. In addition, the power input needed to reach the operating temperature is decreased by 15% compared to the original design. 3D simulations are performed to show that the changes made in the 2D case give similar results for the real 3D case.

    Place, publisher, year, edition, pages
    ScienceDirect, 2002
    Keywords
    A1. Computer simulation, A1. Heat transfer, A3. Chemical, vapor deposition, A3. Hot-wall epitaxy, B2. Semiconducting silicon carbide
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15064 (URN)10.1016/S0022-0248(01)01831-0 (DOI)
    Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
    6. Growth of high quality AlN Epitaxial Films by Hot-Wall Chemical Vapour Deposition
    Open this publication in new window or tab >>Growth of high quality AlN Epitaxial Films by Hot-Wall Chemical Vapour Deposition
    Show others...
    1998 (English)In: Proceedings of the International Conference on Silicon Carbide, III-Nitrides and Related Materials, 1997, 1998, Vol. 264-268, p. 1133-1136Conference paper, Published paper (Refereed)
    Abstract [en]

    Epitaxial films of high quality AlN have been grown on SiC substrates at 1200 °C and 1450 °C, using a hot-wall CVD reactor. The thickness of the epitaxial layers were measured using room temperature infrared reflectance. To verify the crystal quality, X-ray diffraction (XRD) rocking curves of the ALN 0002 peak were measured. A 250 Å thick film grown at 1450°C had a full width half maximum (FWHM) of 42 arcsec, whereas a 1000 Å thick film grown at 1200 °C had a FWHM of 100 arcsec. A TEM image of the sample grown at the lower temperature showed thickness of around 950 Å, thereby verifying the infrared reflectance measurements. We conclude that the higher temperature the better the crystal quality we obtain.

     

    Keywords
    Hot-Wall CVD, Thin Film, XRD, TEM, Infrared reflectance
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15065 (URN)
    Conference
    International Conference on Silicon Carbide, III-Nitrides and Related Materials, 1997
    Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2013-06-12Bibliographically approved
    7. Infrared Reflectance of Extremely Thin AlN Epi Films Deposited on SiC Substrates
    Open this publication in new window or tab >>Infrared Reflectance of Extremely Thin AlN Epi Films Deposited on SiC Substrates
    Show others...
    1998 (English)In: Materials Science Forum Vols. 264-268, 1998, Vol. 264-268, p. 649-652Conference paper, Published paper (Refereed)
    Abstract [en]

    The room temperature reflectance of thin (£ 1000Å) AlN epi-films deposited on n type 6H SiC has been measure. These epi-films are too thin to produce interference fringes, from which epi-films thickness is often extracted, within the measured spectral region. However, features from the AlN reststrahl reflectance band can be clearly seen for AlN epi-films as thin as 250Å. Thicknesses are extracted from the measured spectra by comparing them directly to calculated spectra with the epi-film thickness being the only fitting parameter. The accuracy of these thickness determinations is confirmed by comparing them to thickness measured on samples studied by cross sectional TEM.

    Keywords
    Epi-film Thickness, Reflectance, TEM
    National Category
    Other Engineering and Technologies not elsewhere specified
    Identifiers
    urn:nbn:se:liu:diva-15066 (URN)
    Conference
    Conference on Silicon Carbide, III-Nitrides and Related Materials, 1997
    Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2016-08-31Bibliographically approved
  • 21.
    Forsberg, Urban
    et al.
    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.
    MacMillan, M. F.
    Persson, P. O. Å.
    Linköping University, Department of Physics, Chemistry and Biology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth of high quality AlN Epitaxial Films by Hot-Wall Chemical Vapour Deposition1998In: Proceedings of the International Conference on Silicon Carbide, III-Nitrides and Related Materials, 1997, 1998, Vol. 264-268, p. 1133-1136Conference paper (Refereed)
    Abstract [en]

    Epitaxial films of high quality AlN have been grown on SiC substrates at 1200 °C and 1450 °C, using a hot-wall CVD reactor. The thickness of the epitaxial layers were measured using room temperature infrared reflectance. To verify the crystal quality, X-ray diffraction (XRD) rocking curves of the ALN 0002 peak were measured. A 250 Å thick film grown at 1450°C had a full width half maximum (FWHM) of 42 arcsec, whereas a 1000 Å thick film grown at 1200 °C had a FWHM of 100 arcsec. A TEM image of the sample grown at the lower temperature showed thickness of around 950 Å, thereby verifying the infrared reflectance measurements. We conclude that the higher temperature the better the crystal quality we obtain.

     

  • 22.
    Forsberg, Urban
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Linnarsson, M. K.
    Solid State Electronics, Royal Institute of Technology, SE-164 40 Kista, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nitrogen doping of epitaxial Silicon Carbide2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 236, no 1-3, p. 101-112Article in journal (Refereed)
    Abstract [en]

    Intentional doping with nitrogen of 4H- and 6H-SiC has been performed using a hot-wall CVD reactor. The nitrogen doping dependence on the temperature, pressure, C/Si ratio, growth rate and nitrogen flow has been investigated. The nitrogen incorporation for C-face material showed to be C/Si ratio independent, whereas the doping decreased with increasing C/Si ratio for the Si-face material in accordance with the “site-competition” model. The nitrogen incorporation was constant in a temperature “window” of 75°C on Si-face material indicating a mass transport limited incorporation. Increasing the growth rate resulted in a decrease of nitrogen incorporation on Si-face but an increase on C-face material. Finally, a comparison between previously published results on cold-wall CVD-grown material and the present hot-wall-grown material is presented.

  • 23.
    Forsberg, Urban
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Linnarsson, M. K.
    Solid State Electronics, Royal Institute of Technology, SE-164 40, Kista, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Aluminum doping of epitaxial Silicon Carbide2003In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, p. 340-350Article in journal (Refereed)
    Abstract [en]

    Intentional doping of aluminum in 4H and 6H SiC has been performed using a hot-wall CVD reactor. The dependence of aluminum incorporation on temperature, pressure, C/Si ratio, growth rate, and TMA flow has been investigated. The aluminum incorporation showed to be polarity dependent. The high aluminum incorporation on the Si-face is closely related to the carbon coverage on the SiC surface. Changes in process parameters changes the effective C/Si ratio close to the SiC surface. Increased growth rate and C/Si ratio increases the aluminum incorporation on the Si-face. Diffusion limited incorporation occurs at high growth rate. Reduced pressure increases the effective C/Si ratio, and at low growth rate, the aluminum incorporation increases initially, levels off at a critical pressure, and continues to decrease below the critical pressure. The aluminum incorporation showed to be constant in a temperature range of 50°C. The highest atomic concentration of aluminum observed in this study was 3×1017 and 8×1018 cm−3 in Si and C-face, respectively.

  • 24.
    Forsberg, Urban
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Linnarsson, MK
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Swedish Royal Institute of Technolology, Kista, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Aluminum doping of epitaxial silicon carbide grown by hot-wall CVD, Effect of process parameters2002In: Proceedings of the International Conference on Silicon Carbide and Related Materials, Tsukuba, 2001 / [ed] S. Yoshida, S. Nishino, H. Harima and T. Kimoto, 2002, Vol. 389-3, p. 203-206Conference paper (Refereed)
    Abstract [en]

    Intentional doping of aluminum in 4H and 6H SiC has been performed using a hot-wall CVD reactor. The dependence of aluminum incorporation on temperature, pressure, C/Si ratio, growth rate, and TMA flow has been investigated. The aluminum incorporation showed to be polarity dependent. The high aluminum incorporation on the Si-face is closely related to the carbon coverage on the SiC surface. Changes in process parameters changes the effective C/Si ratio close to the SiC surface. Increased growth rate and C/Si ratio increases the aluminum incorporation on the Si-face. Diffusion limited incorporation occurs at high growth rate. Reduced pressure increases the effective C/Si ratio, and at low growth rate, the aluminum incorporation increases initially, levels off at a critical pressure, and continues to decrease below the critical pressure. The aluminum incorporation showed to be constant in a temperature range of 50°C. The highest atomic concentration of aluminum observed in this study was 3·1017 and 8·1018 cm-3 in Si and C-face, respectively.

  • 25.
    Forsberg, Urban
    et al.
    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.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Linnarsson, M.K.
    Royal Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapour deposition2001In: Proc. of the MRS Spring Meeting 2001, 680E, 2001Conference paper (Refereed)
  • 26.
    Forsberg, Urban
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Linnarsson, MK
    Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden ABB Corp Res, SE-72178 Vasteras, Sweden Royal Inst Technol, SE-16440 Kista, Sweden.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Photoluminescence study of CVD layers highly doped with nitrogen2000In: Materials Science Forum, Vols. 338-342, 2000, Vol. 338-342, p. 619-622Conference paper (Refereed)
    Abstract [en]

    From a systematic study of highly doped n-type 4H-SiC epilayers we observe a photoluminescence spectrum, which was previously associated with the recombination of a bound exciton at the neutral boron acceptor. Electrical measurements performed on these layers show clearly n-type conductivity. It was feasible to dope and measure reproducibly the layers from low 10(17) to mid 10(18) cm(-3). It was not possible to determine the doping from Capacitance Voltage measurements for the samples grown with the highest doping (>6.10(18) cm(-3)). However Secondary Ion Mass spectrometry did not reveal any boron impurities in the layers and shows good agreement with electrical measurements regarding the nitrogen concentration.

  • 27.
    Forsberg, Urban
    et al.
    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.
    Rorsman, N.
    Linköping University, Department of Physics, Chemistry and Biology.
    Eriksson, J.
    Linnarsson, M. K.
    Solid State Electronics, Royal Institute of Technology, SE-164 40 Kista, Sweden.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology.
    Storasta, Liutauras
    Linköping University, Department of Physics, Chemistry and Biology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Growth and characterisation 4H-SiC MESFET structures grown by Hot-Wall CVD2001In: Proc. of the MRS 2000 Fall Meeting, 2001, p. H2.3.2-Conference paper (Refereed)
    Abstract [en]

    Metal semiconductor field effect transistor structures have been grown in a hot-wall CVD reactor. Using trimethylaluminium and nitrogen, p- and n-type epitaxial layers were grown on semi insulating substrates. A comprehensive characterization study of thickness and doping of these multi structures has been performed by using scanning electron microscopy , secondary ion mass spectrometry, capacitance-voltage and low temperature photoluminescence. Optimisation of growth parameters has resulted in very abrupt doping profiles. The grown metal semiconductor field effect transistor structures have been processed and parts of the transistor properties are presented.

  • 28.
    Forsberg, Urban
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ivanov, Ivan Gueorguiev
    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.
    Hot-wall MOCVD growth and characterization of III-nitrides for HEMT application2006In: WOCSDICE 2006,2006, 2006Conference paper (Other academic)
  • 29.
    Forsberg, Urban
    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.
    Kakanakova-Georgieva, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ciechonski, Rafal
    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.
    Improved hot-wall MOCVD growth of highly uniform AlGaN/GaN/HEMT structures2009In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 10, p. 3007-3010Article in journal (Refereed)
    Abstract [en]

    The inherent advantages of the hot-wall metal organic chemical vapor deposition (MOCVD) reactor (low temperature gradients, less bowing of the wafer during growth, efficient precursor cracking) compared to a cold-wall reactor make it easier to obtain uniform growth. However, arcing may occur in the growth chamber during growth, which deteriorates the properties of the grown material. By inserting insulating pyrolytic BN (PBN) stripes in the growth chamber we have completely eliminated this problem. Using this novel approach we have grown highly uniform, advanced high electron mobility transistor (HEMT) structures on 4 semi-insulating (SI) SiC substrates with gas-foil rotation of the substrate. The nonuniformities of sheet resistance and epilayer thickness are typically less than 3% over the wafer. The room temperature hall mobility of the 2DEG is well above 2000 cm(2)/V s and the sheet resistance about 270 Omega/sqr.

  • 30.
    Gustafsson, Sebastian
    et al.
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Bergsten, Johan
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Thorsell, Mattias
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Rorsman, Niklas
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg, Sweden.
    Dispersive Effects in Microwave AlGaN/AlN/GaN HEMTs With Carbon-Doped Buffer2015In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 62, no 7, p. 2162-2169Article in journal (Refereed)
    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.

  • 31.
    Henry, Anne
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ellison, A
    Linkoping Univ, Dept Phys & Measurement Technol, SE-58183 Linkoping, Sweden Okmet AB, SE-58330 Linkoping, Sweden.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Magnusson, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pozina, Galia
    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.
    Characterization of bulk and epitaxial SiC material using photoluminescence spectroscopy2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 593-596Conference paper (Refereed)
    Abstract [en]

    We are using low temperature photoluminescence (LTPL) to evaluate the quality of SiC wafers and are able to characterize up to 2 inch diameter wafers (with or without epilayers) at low temperature (2K). Polytype maps for bulk material can be drawn, as well as nitrogen concentration maps for both bulk and epilayer wafers in the very large doping range available today (from low 10(14) cm(-3) to 10(19) cm(-3)).

  • 32.
    Henry, Anne
    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.
    Linnarsson, M. K.
    Solid State Electronics, Royal Institute of Technology, SE-164 40 Kista, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Determination of nitrogen doping concentration in doped 4H-SiC epilayers by low temperature photoluminescence2005In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, no 2-3, p. 254-257Article in journal (Refereed)
    Abstract [en]

    A complete calibration of nitrogen concentration in doped 4H-SiC material is presented. This is done in the very large range of doping available today, i.e. from low 1014 to 1019 cm-3. The samples are 4H-SiC films fabricated by hot-wall chemical vapour deposition. Low temperature photoluminescence is used as the experimental tool. For doping concentrations less than 8 × 1017 cm-3 comparison between the intensity of various luminescence lines is used, whereas for doping higher than 3 × 1018 cm-3 the energy position of an observed broad band allows the determination of the doping level.

  • 33.
    Henry, Anne
    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.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Ivanov, Ivan
    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.
    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.
    AlGaN Multiple Quantum Wells and AlN Grown in a Hot-wall MOCVD for Deep UV Applications2009In: ECS Transactions, Vol. 25, Iss. 8, ECS , 2009, p. 837-844Conference paper (Refereed)
    Abstract [en]

    AlxGa1-xN multiple quantum wells (MQW) were grown on AlN epilayer grown on 4H-SiC substrate. The growth was performed without interruption in a horizontal hot-wall MOCVD reactor using a mixture of hydrogen and nitrogen as carrier gases. The precursors were ammonia, trimethylaluminum and trimethylgallium. Results obtained from X-ray diffraction and infra-red reflectance were used to obtain the composition of the films when growing simple AlxGa1 xN layer. Visible reflectance was used to evaluate the thickness of the films. Finally the MQW parameters as thicknesses and composition variation were obtained by scanning transmission electron microscopy and demonstrated an agreement with the growth parameters used

  • 34.
    Hofmann, T.
    et al.
    University of Nebraska, USA .
    Kuehne, P.
    University of Nebraska, USA .
    Schöche, S.
    University of Nebraska, USA .
    Chen, Jr-Tai
    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.
    Ben Sedrine, N.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Health Sciences.
    Herzinger, C. M
    JA Woollam Co Inc, USA .
    Woollam, J. A
    JA Woollam Co Inc, USA .
    Schubert, M.
    University of Nebraska, USA .
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Temperature dependent effective mass in AlGaN/GaN high electron mobility transistor structures2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 19Article in journal (Refereed)
    Abstract [en]

    The temperature-dependence of free-charge carrier mobility, sheet density, and effective mass of a two-dimensional electron gas in a AlGaN/GaN heterostructure deposited on SiC substrate is determined using the THz optical Hall effect in the spectral range from 0.22 to 0.32 THz for temperatures from 1.5 to 300 K. The THz optical Hall-effect measurements are combined with room temperature mid-infrared spectroscopic ellipsometry measurements to determine the layer thickness, phonon mode, and free-charge carrier parameters of the heterostructure constituents. An increase of the electron effective mass from (0.22 +/- 0.01)m(0) at 1.5 K to (0.36 +/- 0.03)m(0) at 300 K is observed, which is indicative for a reduction in spatial confinement of the two-dimensional electron gas at room temperature. The temperature-dependence of the mobility and the sheet density is in good agreement with electrical measurements reported in the literature.

  • 35.
    Holtz, Per Olof
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hsu, Chi-Wei
    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.
    Karlsson, K. Fredrik
    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.
    Deterministic Single InGaN Quantum Dots grown on GaN Micro-Pyramid Arrays2013In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 646, p. 34-37Article in journal (Other academic)
    Abstract [en]

    InGaN quantum dots (QDs) formed on top of GaN pyramids have been fabricated by means of selective area growth employing hot wall MOCVD. Upon regrowth of a patterned substrate, the growth will solely occur in the holes, which evolve into epitaxially grown wurtzite based pyramids. These pyramids are subsequently overgrown by a thin optically active InGaN well. The QDs are preferably nucleating at the apices of the pyramids as evidenced by the transmission electron microscopy (TEM). The emission from these QDs have been monitored by means of microphotoluminescence (µPL), in which single emission lines have been detected with a sub-meV line width. The µPL measurements undoubtedly reveal that the QDs are located in the apexes of the pyramids, since the sharp emission peaks can only be monitored as the excitation laser is focused on the apices in the µPL. It is also demonstrated that the emission energy can be changed in a controlled way by altering the growth conditions, like the growth temperature and/or composition, for the InGaN layers. The tip of the GaN pyramid is on the nm scale and can be made sharp or slightly truncated. TEM analysis combined with µPL results strongly indicate that the Stranski-Krastanow growth modepreferably is taking place at the microscopic c-plane truncation of the GaN pyramid. Single emission lines with a high degree of polarization is a common feature observed for individual QDs. This emission remains unchanged with increasing the excitation power and sample temperature. An in-plane elongated QD forming a shallow potential with an equal number of electrons and holes is proposed to explain the observed characteristics of merely a single exciton emission with a high degree of polarization.

  • 36.
    Holtz, Per-Olof
    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.
    Larsson, L A
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Karlsson, K Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Dufåker, Daniel
    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.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Moskalenko, Evgenii
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Dimastrodonato, V
    National University of Ireland University of Coll Cork.
    Mereni, L
    National University of Ireland University of Coll Cork.
    Pelucchi, E
    National University of Ireland University of Coll Cork.
    Optical characterization of individual quantum dots2012In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 407, no 10, p. 1472-1475Article in journal (Refereed)
    Abstract [en]

    Optical characterization of single quantum dots (QDs) by means of micro-photoluminescence (mu PL) will be reviewed. Both QDs formed in the Stranski-Krastanov mode as well as dots in the apex of pyramidal structures will be presented. For InGaAs/GaAs dots, several excitonic features with different charge states will be demonstrated. By varying the magnitude of an external electric or magnetic field and/or the temperature, it has been demonstrated that the transportation of carriers is affected and accordingly the charge state of a single QD can be tuned. In addition, we have shown that the charge state of the QD can be controlled also by pure optical means, i.e. by altering the photo excitation conditions. Based on the experience of the developed InAs/GaAs QD system, similar methods have been applied on the InGaN/GaN QD system. less thanbrgreater than less thanbrgreater thanThe coupling of LO phonons to the QD emission is experimentally examined for both charged and neutral excitons in single InGaAs/GaAs QDs in the apex of pyramidal structures. It is shown that the positively charged exciton exhibits a significantly weaker LO phonon coupling in the mu PL spectra than the neutral and negatively charged species, a fact, which is in consistency with model simulations performed.

  • 37.
    Hsu, Chih-Wei
    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.
    Karlsson, Fredrik
    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.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Optical characterization of InGaN quantum dots on GaN pyramids grown by MOCVD2010Conference paper (Refereed)
  • 38.
    Hsu, Chih-Wei
    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.
    Karlsson, Fredrik
    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.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Single Excitons in InGaN Quantum Dots on GaN Pyramid Arrays2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 6, p. 2415-2418Article in journal (Refereed)
    Abstract [en]

    Fabrication of single InGaN quantum dots (QDs) on top of GaN micropyramids is reported. The formation of single QDs is evidenced by showing single sub-millielectronvolt emission lines in microphotoluminescence (mu PL) spectra. Tunable QD emission energy by varying the growth temperature of the InGaN layers is also demonstrated. From mu PL, it is evident that the QDs are located in the apexes of the pyramids. The fact that the emission lines of the QDs are linear polarized in a preferred direction implies that the apexes induce unidirected anisotropic fields to the QDs. The single emission lines remain unchanged with increasing the excitation power and/or crystal temperature. An in-plane elongated QD forming a shallow potential with an equal number of trapped electrons and holes is proposed to explain the absence of other exciton complexes.

  • 39.
    Hsu, Chih-Wei
    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.
    Palisaitis, Justinas
    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.
    Karlsson, K. Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. 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.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Controlled Growth of GaN Pyramidal template hosting InGaN Quantum DotsManuscript (preprint) (Other academic)
    Abstract [en]

    The emission properties of InGaN grown on hexagonal GaN pyramids with various pitch distances (PD) are studied. Emissions associated with InGaN quantum wells (QWs) and InGaN quantum dots (QDs) can be identified. The emission energies of InGaN QWs and QDs shift toward opposite directions with increasing PD; red-shift for QWs and blue-shift for QDs. Based on the source supply mechanism in a selective area growth process, the formation of InGaN QDs on GaN pyramids is believed to be a combined effect of Stranski-Krastanow growth mode and spinodal decomposition taking place at the microscopic (0001) surfaces on GaN pyramids.

  • 40.
    Hsu, Chih-Wei
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Moskalenko, Evgenii
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Eriksson, Martin
    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.
    Karlsson, Fredrik K.
    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.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    The charged exciton in an InGaN quantum dot on a GaN pyramid2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 1Article in journal (Refereed)
    Abstract [en]

    The emission of a charged exciton in an InGaN quantum dot (QD) on top of a GaN pyramid is identified experimentally. The intensity of the charged exciton exhibits the expected competition with that of the single exciton, as observed in temperature-dependent micro-photoluminescence measurements, performed with different excitation energies. The non-zero charge state of this complex is further supported by time resolved micro-photoluminescence measurements, which excludes neutral alternatives of biexciton. The potential fluctuations in the vicinity of the QD that localizes the charge carriers are proposed to be responsible for the unequal supply of electrons and holes into the QD.

  • 41.
    Hsu, Hsu-Cheng
    et al.
    National Cheng Kung University, Taiwan National Cheng Kung University, Taiwan .
    Hsu, Geng-Ming
    National Taiwan University, Taiwan .
    Lai, Yu-shiung
    National Taiwan University, Taiwan .
    Chuan Feng, Zhe
    National Taiwan University, Taiwan .
    Tseng, Shuo-Yen
    National Cheng Kung University, Taiwan National Cheng Kung University, Taiwan .
    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.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Chen, Kuei-Hsien
    National Taiwan University, Taiwan Academic Sinica, Taiwan .
    Chen, Li-Chyong
    National Taiwan University, Taiwan .
    Polarized and diameter-dependent Raman scattering from individual aluminum nitride nanowires: The antenna and cavity effects2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 12, p. 121902-Article in journal (Refereed)
    Abstract [en]

    Raman scattering of individual aluminum nitride (AlN) nanowires is investigated systematically. The axial direction of single nanowire can be rapidly verified by polarized Raman scattering. The angular dependencies of E-2(high) mode show strongly anisotropic behavior in smaller nanowires, which results from optical antenna effect. Raman enhancement (RE) per unit volume of E-2(high) increases with decreasing diameter of nanowires. Compared to the thin film, similar to 200-fold increase of RE is observed in AlN nanowires having diameter less than 50 nm, which is far beyond the quantum confinement regime. Such a large RE can be attributed to the effects of resonant cavity and stimulated Raman scattering.

  • 42.
    J T Simms, R J T
    et al.
    University of Bristol.
    Uren, M J
    QinetiQ Ltd.
    Martin, T
    QinetiQ Ltd.
    Powell, J
    QinetiQ Ltd.
    Forsberg, Urban
    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.
    Kakanakova-Georgieva, Anelia
    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.
    Kuball, M
    University of Bristol.
    Micro-Raman spectroscopy as a voltage probe in AlGaN/GaN heterostructure devices: Determination of buffer resistances2011In: SOLID-STATE ELECTRONICS, ISSN 0038-1101, Vol. 55, no 1, p. 5-7Article in journal (Refereed)
    Abstract [en]

    A time-resolved micro-Raman technique was developed to probe the transient voltage in the GaN buffer layer of AlGaN/GaN heterostructure devices. The transient potential distribution under Ohmic contacts of devices behaved like a capacitance-resistance coupled network, with a decrease in amplitude and phase shift of the potential as a function of operating voltage frequency. This phenomenon was used to extract a value of 0.6 M Omega/square for sheet resistance of the AIN nucleation layer at the GaN/SiC interface from the characteristic RC value of the network. This demonstrates the effectiveness of this voltage probe technique as a non-invasive method of characterizing nucleation layers.

  • 43.
    Janson, M. S.
    et al.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Linnarsson, M. K.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Hallen, A.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Svensson, B. G.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Achtziger, N.
    Univ Jena, Inst Festkorperphys, D-07743 Jena, Germany .
    Unéus, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hydrogen in the wide bandgap semiconductor silicon carbide2004In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T108, p. 99-112Article in journal (Refereed)
    Abstract [en]

    In this paper we give a review of our recent results related to the incorporation of hydrogen (H) in silicon carbide (SiC) and its interaction with acceptor doping atoms and implantation induced defects. Hydrogen is an abundant impurity in the growth of epitaxial SiC since it is present in the precursor gases and since H-2 is used as the carrier gas. High concentrations of hydrogen are indeed incorporated into highly doped p-type epi-layers and it is shown that the main source is the carrier gas. Furthermore, it is revealed that the entire substrate becomes homogeneously filled with hydrogen during growth and that this hydrogen is more thermally stable than that in the epi-layer. Incorporation of hydrogen from an H-2 ambient, at temperatures considerably lower than those used for epitaxy, is also demonstrated in p-type samples coated with a catalytic metal film. This effect is most likely the cause for the increased series resistance observed in p-type SiC Schottky sensor devices using a catalytic metal gate after annealing at 600 degrees C in a H-2 containing ambient. Hydrogen is found to passivate the acceptors Al and B by forming electrically neutral H-acceptor complexes. Unlike in Si and GaAs, the two H-acceptor complexes in SiC exhibit very different dissociation energies, suggesting that the atomic configurations of the complexes are significantly different. The migration of mobile hydrogen in the presence of externally applied, or internal built-in, electric fields further reveals that hydrogen is present as H+ in p-type SiC. Finally, the redistribution and subsequent out-diffusion of low energy implanted H-1 and H-2 is investigated. Two annealing phases for the redistribution are observed, and the activation energies for the processes are extracted.

  • 44.
    Janzén, Erik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Danielsson, Örjan
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hallin, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    ul-Hassan, Jawad
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Henry, Anne
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ivanov, Ivan Gueorguiev
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Kakanakova-Gueorguie, Anelia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Persson, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Wahab, Qamar Ul
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    SiC and III-nitride Growth in a Hot-wall CVD Reactor2005In: Materials Science Forum, ISSN 0255-5476, volume 483-485, Trans Tech Publications , 2005, Vol. 483-485, p. 61-66Conference paper (Refereed)
  • 45. Kakanakova-Georgieva, A
    et al.
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Hallin, Christer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Persson, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Storasta, Liutauras
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Pozina, Galia
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Birch, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Implementation of hot-wall MOCVD in the growth of high-quality GaN on SiC2003In: Materials Science Forum, Vols. 433-436, Trans Tech Publications , 2003, Vol. 433-4, p. 991-994Conference paper (Refereed)
    Abstract [en]

    This paper reports on the growth of high-quality GaN layers on SiC substrates by hotwall MOCVD. Use of AlN buffer with a thickness exceeding 50 nm is employed for the GaN deposition and it is found to encompass most of the misfit defects. A narrower X-ray rocking curve over asymmetric than over symmetric reflection is measured - full width at a half maximum (FWHM) of 350 arcsec vs. FWHM of 490 arcsec for 10.4 and 00.2 peaks, respectively, indicating high overall quality of the film. The free exciton photoluminescence emission peak has rather narrow FWHM of 5 meV. The typical thickness of the GaN layers is about 2 mum and they are completely depleted according to the capacitance-voltage profiling, which corresponds to estimated residual doping of less than 5x10(14) cm(-3). Only in some cases when the GaN layer is not depleted, deep level transient spectroscopy is performed and two deep traps with activation energies of 0.26 and 0.59 eV below the conduction band are measured.

  • 46.
    Kakanakova-Georgieva, Anelia
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Ciechonski, Rafal
    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.
    Lundskog, Anders
    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.
    Hot-Wall MOCVD for Highly Efficient and Uniform Growth of AIN2009In: Crystal Growth & Design, ISSN 1528-7483, Vol. 9, no 2, p. 880-884Article in journal (Refereed)
    Abstract [en]

    We demonstrated successful growth of AIN at a temperature of 1200 degrees C in a set of hot-wall MOCVD systems with the possibility of straightforward scaling up the process on larger wafer areas to meet the demand of device technologies. We outlined several aspects of the carefully optimized design and process parameters with relevance to achievement of a high overall growth rate (1 and up to 2 mu m/h), efficiency, and uniformity, which to a great extent depends on how consumption of growth-limiting species by gas-phase adduct formation can actively be prevented. Mixing of the precursors upstream from the deposition area facilitates uniform epitaxial growth, while the greater uniformity of substrate temperature inherent to the hot-wall reactor and rotation of the wafer are of fundamental importance for layer-growth uniformity. The AIN layer thickness can be controlled with an accuracy of +/- 1.3% on 2 in. wafers. The low-temperature cathodoluminescence spectrum of the AIN epitaxial material is strongly dominated by the intense near band-gap deep UV emission at about 208 nm.

  • 47.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Ivanov, Ivan Gueorguiev
    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.
    Hot-wall MOCVD developments towards 2 inch AlGaN/GaN epitaxial growth2006In: ICMOVPE2006,2006, 2006Conference paper (Other academic)
  • 48.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Ivanov, Ivan Gueorguiev
    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.
    Uniform hot-wall MOCVD epitaxial growth of 2 inch AlGaN/GaN HEMT structures2007In: Journal of Crystal Growth, Vol. 300, 2007, Vol. 300, no 1, p. 100-103Conference paper (Refereed)
    Abstract [en]

    The hot-wall metalorganic chemical vapor deposition (MOCVD) concept has been applied to the growth of AlxGa1-xN/GaN high electron mobility transistor (HEMT) device heterostructures on 2 inch 4H-SiC wafers. Due to the small vertical and horizontal temperature gradients inherent to the hot-wall MOCVD concept the variations of all properties of a typical HEMT heterostructure are very small over the wafer: GaN buffer layer thickness of 1.83 μm±1%, Al content of the AlxGa1-xN barrier of 27.7±0.1%, AlxGa1-xN barrier thickness of 25 nm±4%, sheet carrier density of 1.05×1013 cm-2±4%, pinch-off voltage of -5.3 V±3%, and sheet resistance of 449 Ω±1%.

  • 49.
    Kakanakova-Georgieva, Anelia
    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.
    Carbon-tuned cathodoluminescence of semi-insulating GaN2011In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, ISSN 1862-6300, Vol. 208, no 9, p. 2182-2185Article in journal (Refereed)
    Abstract [en]

    We report on the cathodoluminescence (CL) of nominally undoped semi-insulating GaN layers grown by hot-wall metal-organic chemical vapor deposition (MOCVD) at a threefold increase of the growth rate limited by the TMGa flow. The growth kinetics is such, that C is the only background impurity in the layers with controllably increasing concentration from 5 x 10(16) to 6 x 10(17) cm(-3), while other background impurities, H. O and Si, are essentially at the SIMS detection levels. The hot-wall MOCVD is not an ordinary approach to GaN growth process and this study corroborates a more perceptive outlook on the C incorporation in GaN and any potential C-incorporation-mediated luminescence, including the observed here blue luminescence (BL) at similar to 417 nm, and the yellow luminescence (YL) with shifting peak position towards shorter wavelengths, similar to 555-543-525 nm.

  • 50.
    Kakanakova-Georgieva, Anelia
    et al.
    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.
    Magnusson, Björn
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Yakimova, Rositsa
    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.
    Growth of AlN films by hot-wall CVD and sublimation techniques: Effect of growth cell pressure2002In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1469-1472Conference paper (Refereed)
    Abstract [en]

    Aluminum nitride (AlN) films were grown on off-axis, Si-terminated 4H-SiC substrates by hot-wall CVD and sublimation techniques. The films were investigated by Infrared reflectance, Optical microscopy, Energy Dispersive X-ray analysis and Cathodoluminescence in a Scanning Electron Microscope with respect to their thickness, morphological, compositional and luminescence properties, in order to examine the influence of the growth cell pressure in either of the two deposition methods. Good quality thick AlN films were obtained by hot-wall CVD at temperature of 1200degreesC and reduced pressure of 100 mbar as reflected in the near stoichiometric N/Al ratio in these layers and in the appearance of the characteristic AlN near band edge emission. The AlN sublimation grown films at temperature of 2100degreesC suffered from island growth irrespective of the background pressure. The supersaturation conditions that affect strongly the growth mode became more favorable when the temperature was reduced to 1900degreesC.

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