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  • 1.
    Armakavicius, Nerijus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Chen, Jr-Tai
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hofmann, Tino
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, USA.
    Knight, Sean
    Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, USA.
    Kuhne, Philipp
    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.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Properties of two-dimensional electron gas in AlGaN/GaN HEMT structures determined by cavity-enhanced THz optical Hall effect2016In: Physica Status Solidi C-Current Topics in Solid State Physics, Vol 13 No 5-6, Wiley-VCH Verlagsgesellschaft, 2016, Vol. 13, no 5-6, p. 369-373Conference paper (Refereed)
    Abstract [en]

    In this work we employ terahertz (THz) ellipsometry to determine two-dimensional electron gas (2DEG) density, mobility and effective mass in AlGaN/GaN high electron mobility transistor structures grown on 4H-SiC substrates. The effect of the GaN interface exposure to low-flow-rate trimethylaluminum (TMA) on the 2DEG properties is studied. The 2DEG effective mass and sheet density are determined tobe in the range of 0.30-0.32m0 and 4.3-5.5×1012 cm–2, respectively. The 2DEG effective mass parameters are found to be higher than the bulk effective mass of GaN, which is discussed in view of 2DEG confinement. It is shown that exposure to TMA flow improves the 2DEG mobility from 2000 cm2/Vs to values above 2200 cm2/Vs. A record mobility of 2332±61 cm2/Vs is determined for the sample with GaN interface exposed to TMA for 30 s. This improvement in mobility is suggested to be due to AlGaN/GaN interface sharpening causing the reduction of interface roughness scattering of electrons in the 2DEG.

  • 2.
    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.

  • 3.
    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.

  • 4.
    Kakanakova-Georgieva, Anelia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Stattin, M
    Chalmers.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Haglund, Å
    Chalmers.
    Larsson, A
    Chalmers.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Mg-doped Al0.85Ga0.15N layers grown by hot-wall MOCVD with low resistivity at room temperature2010In: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, ISSN 1862-6254, Vol. 4, no 11, p. 311-313Article in journal (Refereed)
    Abstract [en]

    We report on the hot-wall MOCVD growth of Mg-doped AlxGa1-xN layers with an Al content as high as x similar to 0.85. After subjecting the layers to post-growth in-situ annealing in nitrogen in the growth reactor, a room temperature resistivity of 7 k Omega cm was obtained indicating an enhanced p-type conductivity compared to published data for AlxGa1-xN layers with a lower Al content of x similar to 0.70 and a room temperature resistivity of about 10 k Omega cm. It is believed that the enhanced p-type conductivity is a result of reduced compensation by native defects through growth conditions enabled by the distinct hot-wall MOCVD system.

  • 5.
    Kakanakova-Georgieva, Anelia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Trinh, Xuan Thang
    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.
    Nguyen, Son Tien
    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.
    The complex impact of silicon and oxygen on the n-type conductivity of high-Al-content AlGaN2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 13, p. 132113-Article in journal (Refereed)
    Abstract [en]

    Issues of major relevance to the n-type conductivity of Al0.77Ga0.23N associated with Si and O incorporation, their shallow donor or deep donor level behavior, and carrier compensation are elucidated by allying (i) study of Si and O incorporation kinetics at high process temperature and low growth rate, and (ii) electron paramagnetic resonance measurements. The Al0.77Ga0.23N composition correlates to that Al content for which a drastic reduction of the conductivity of AlxGa1−xN is commonly reported. We note the incorporation of carbon, the role of which for the transport properties of AlxGa1−xN has not been widely discussed.

  • 6.
    Kakanakova-Gueorgieva, Anelia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    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-quality AlN layers grown by hot-wall MOCVD at reduced temperatures2012In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 338, no 1, p. 52-56Article in journal (Refereed)
    Abstract [en]

    We report on a growth of AlN at reduced temperatures of 1100 C and 1200 C in a horizontal-tube hot-wall metalorganic chemical vapor deposition reactor configured for operation at temperatures of up to 15001600 C and using a joint delivery of precursors. We present a simple route - as viewed in the context of the elaborate multilayer growth approaches with pulsed ammonia supply - for the AlN growth process on SiC substrates at the reduced temperature of 1200 C. The established growth conditions in conjunction with the particular in-situ intervening SiC substrate treatment are considered pertinent to the accomplishment of crystalline, relatively thin, ∼700 nm, single AlN layers of high-quality. The feedback is obtained from surface morphology, cathodoluminescence and secondary ion mass spectrometry characterization.

  • 7.
    Kakanakova-Gueorguie, Anelia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Trinh, Xuan Thang
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    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.
    Silicon and oxygen in high-Al-content AlGaN: incorporation kinetics and electron paramagnetic resonance study2014In: Gettering and Defect Engineering in Semiconductor Technology XV, Trans Tech Publications Inc., 2014, Vol. 205-206, p. 441-445Conference paper (Refereed)
    Abstract [en]

    The high-Al-content AlxGa1-xN alloys, xgreater than0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (lambda less than 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in AlxGa1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition.

  • 8.
    Kakanakova-Gueorguie, Anelia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Sahonta, S. -L.
    University of Cambridge, England.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Trinh, Xuan Thang
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Humphreys, C. J.
    University of Cambridge, England.
    n-Type conductivity bound by the growth temperature: the case of Al0.72Ga0.28N highly doped by silicon2016In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, no 35, p. 8291-8296Article in journal (Refereed)
    Abstract [en]

    High-Al-content AlxGa(1-x)N layers, x similar to 0.72, have been grown by metal organic chemical vapour deposition (MOCVD) at a temperature ranging from 1000 to 1100 degrees C, together with high flow rate of the dopant precursor silane (SiH4) in order to obtain highly Si-doped Al0.72Ga0.28N layers, similar to 1 x 10(19) cm(-3) as measured by secondary ion mass spectrometry (SIMS). Further characterization of the layers by capacitance-voltage (C-V), electron paramagnetic resonance (EPR), and transmission electron microscopy (TEM) measurements reveals the complex role of growth temperature for the n-type conductivity of high-Al-content AlxGa1-xN. While increasing temperature is essential for reducing the incorporation of carbon and oxygen impurities in the layers, it also reduces the amount of silicon incorporated as a donor.

  • 9.
    Li, Xun
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Bergsten, J.
    Chalmers, Sweden.
    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.
    Rorsman, N.
    Chalmers, Sweden.
    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.
    Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 26, p. 262105-Article in journal (Refereed)
    Abstract [en]

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 x 10(18) cm(-3)) epitaxial layer closest to the substrate and a lower doped layer (3 x 10(16) cm(-3)) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 x 10(18) cm(-3)) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source. (C) 2015 AIP Publishing LLC.

  • 10.
    Li, Xun
    et al.
    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, Sweden.
    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, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Rorsman, Niklas
    Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Sweden.
    Janzén, Erik
    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, Faculty of Science & Engineering.
    Intentionally carbon doped GaN buffer layer for HEMT application: growth and device results2015Manuscript (preprint) (Other academic)
    Abstract [en]

    The creation of a semi-insulating (SI) buffer layer in AlGaN/GaN HEMT devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). Here we evaluate the use of a carbon precursor, propane, for creating a SI GaN buffer layer. The carbon doping profile obtained from SIMS measurement shows a very uniform incorporation versus depth and no significant memory effect from carbon doping is seen, allowing for the creation of a very abrupt profile. The high carbon doping (1.5×1018 cm-3) does not influence the surface morphology. HRXRD ω rocking curve showed a FWHM of 200 arcsec of the (0002) and 261 arcsec for (10-12) reflection of the GaN, respectively. HEMT devices were processed on the epitaxial layers. An extremely low drain induced barrier lowering value of 0.1 mV/V was measured for a HEMT with a gate length of 0.2 𝜇m. This demonstrates the capability of growing a highly resistive buffer layer using intentional carbon doping.

  • 11.
    Lundskog, Anders
    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.
    Karlsson, K. Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Amloy, Supaluck
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Department of Physics, Faculty of Science, Thaksin University, Thailand.
    Nilsson, Daniel
    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.
    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.
    Direct generation of linearly-polarized photon emission with designated orientations from site-controlled InGaN quantum dots2014In: Light: Science & Applications, ISSN 2095-5545, Vol. 3, article id e139Article in journal (Refereed)
    Abstract [en]

    Semiconductor quantum dots (QDs) have been demonstrated viable for the emission of single photons on demand during the past decade. However, the synthesis of QDs emitting photons with pre-defined and deterministic polarization vectors has proven arduous. The access of linearly-polarized photons is essential for various applications. In this report, a novel concept to directly generate linearly-polarized photons is presented. This concept is based on InGaN QDs grown on top of elongated GaN hexagonal pyramids, by which predefined orientations herald the polarization vectors of the emitted photons from the QDs. This growth scheme should allow fabrication of ultracompact arrays of photon emitters, with a controlled polarization direction for each individual QD emitter.

  • 12.
    Lundskog, Anders
    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.
    Nilsson, Daniel
    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.
    Karlsson, K Fredrik
    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.
    Polarization-controlled photon emission from site-controlled InGaN quantum dotsManuscript (preprint) (Other academic)
    Abstract [en]

    The optical polarization properties of hot-wall MOCVD grown of InGaN quantum dots (QDs) located at the apex of elongated hexagonal GaN pyramids are presented. The QDs showed spectrally narrow and strongly linearly polarized emission lines with average polarization ratios above 0.8 in the microphoto-luminescence spectra. By a comprehensive statistical analysis including more than 1000 InGaN QDs it was concluded that the polarization direction of the QDs follows the spatial elongation of the underlying GaN pyramids when elongated in the <2110> directions.

  • 13.
    Lundskog, Anders
    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.
    Nilsson, Daniel
    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.
    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 hexagonal GaN pyramids by hot-wall MOCVD2013In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 363, p. 287-293Article in journal (Refereed)
    Abstract [en]

    Hexagonal GaN pyramids have been fabricated by hot-wall metal organic chemical vapor deposition (hot-wall MOCVD) and the growth evolution have been studied. It was concluded that the pyramid growth can be divided into two regimes separated by the adsorption kinetics of the {1101} surfaces of the pyramids. In the adsorption regime, the pyramids grow simultaneously in the <1101> and [0001] -directions. In the zero-adsorption regime the pyramids grow only in the [0001] direction. Thus the pyramid growth ceases when the (0001) facet growth has been terminated. Large arrays consisting of highly uniform pyramids with apex radii of 3 nm or less were achieved in the zeroadsorption regime. The growth-regime type was concluded to have a large impact on the uniformity degradation of the pyramids, and their optical properties. The impacts of threading dislocations which enter the pyramid from underneath are also discussed.

  • 14.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Doping of high-Al-content AlGaN grown by MOCVD2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The high-Al-content AlxGa1-xN, x > 0.70, is the principal wide-band-gap alloy system to enable the development of light-emitting diodes operating at the short wavelengths in the deep-ultraviolet, λ < 280 nm. The development of the deep-ultraviolet light-emitting diodes (DUV LEDs) is driven by the social and market impact expected from their implementation in portable units for water disinfection and based on the damaging effect of the deep-ultraviolet radiation on the DNA of various microorganisms. Internationally, intense research and technology developments occur in the past few years, yet, the external quantum efficiency of the DUV LEDs is typically below 1%.

    One of the main material issues in the development of the DUV LEDs is the achievement of n- and ptype doped layers of high-Al-content AlxGa1-xN with low resistivity, which is required for the electrical pumping of the diodes. The doping process, however, becomes significantly more complex with increasing the Al content and the resistivity value can be as high as 101-102 Ω cm for n-type AlN doped by silicon, and 107-108 Ω cm for p-type AlN doped by magnesium.

    The present study is therefore focused on gaining a better understanding of the constraints in the doping process of the high-Al-content AlxGa1-xN alloys, involving mainly the silicon dopant. For this purpose, the epitaxial growth of the high-Al-content AlxGa1-xN and AlN by the implementation of the distinct hot-wall MOCVD is developed in order to achieve layers of good structural and morphological properties, and with low content of residual impurities, particularly oxygen and carbon. Substitutional point defects such as ON and CN may have a profound impact on the doping by their involvement in effects of n-type carrier compensation. The process temperature can be set from 1000 °C and up to 1400 °C in the present study, which is a principal advantage in order to optimize the material properties of the high-Al-content AlxGa1-xN and AlN. The epitaxial growth of the high-Alcontent AlxGa1-xN and AlN is largely performed on 4H-SiC substrates motivated by (i) the lattice mismatch of ~ 1% along the basal plane (the smallest among other available substrates including Si and sapphire), (ii) the good thermal conductivity of 3.7 W cm-1 K-1, which is essential to minimize the self-heating during the operation of any light-emitting diode, and (iii) the limited access to true-bulk AlN wafers. The Si doping is investigated over a large range of [Si] ~ 1×1017 cm-3 - 1×1020 cm-3. Only the high doping range of [Mg] ~ (1-3)×1019 cm-3 is targeted motivated by the large thermal ionization energy of this common acceptor (from 200 meV in GaN to about 630 meV in AlN). The material characterization involves extensive implementation of atomic force microscopy (AFM), x-ray diffraction (XRD), cathodoluminescence (CL), secondary ion mass spectrometry (SIMS), capacitancevoltage measurements, as well as measurements of the conductivity of the layers by contactless microwave-based technique. The possibility to perform electron paramagnetic resonance (EPR) measurements on the Si-doped high-Al-content AlxGa1-xN is essential in order to establish any effect of self-compensation of the shallow donor state of silicon through the related so-called DX state. The EPR measurements corroborate the study of the incorporation kinetics of silicon and oxygen at various process temperatures and growth rates.

    The outcome of this study is accordingly summarized and presents our understanding for (i) the complex impact of silicon and oxygen on the n-type conductivity of Al0.77Ga0.23N, which is the alloy composition at which a drastic reduction of the n-type conductivity of high-Al-content AlxGa1-xN is commonly reported (paper 1); (ii) the strain and morphology compliance during the intentional doping by silicon and magnesium, and its correlation with the resistivity in the highly doped layers of Al0.82Ga0.18N alloy composition (paper2); (iii) the n-type conductivity of highly-Si-doped Al0.72Ga0.28N layers as bound by the process temperature (paper 3); and (iv) the shallow donor or DX behavior of the Si dopant in conductive AlxGa1-xN layers, 0.63 ≤ x ≤ 1 (paper 4). It is noted that the measured n-type conductivity in reference layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition is on par with the state-of-the-art values, i.e. ≤ 0.05 Ω cm, and 0.012 Ω cm, respectively. A room-temperature resistivity of 7 kΩ cm is measured in Mg-doped layers of Al0.85Ga0.15N alloy composition, which is superior to the state-of-art values (paper 5). The performance of the transport properties of the high-Al-content AlxGa1-xN layers is expected to improve with improvement of their material quality. This can be achieved by improvement of the crystalline quality of the AlN-on-SiC template and by the implementation of true-bulk AlN substrates. The AlN heteroepitaxial growth at the process temperatures of 1100-1200 °C is therefore investigated (paper 6). The lattice constants, structural and optical properties of true-bulk, homoepitaxial and heteroepitaxial AlN material grown at high process temperatures of up to 1400 °C is further reported (paper 7).

    List of papers
    1. The complex impact of silicon and oxygen on the n-type conductivity of high-Al-content AlGaN
    Open this publication in new window or tab >>The complex impact of silicon and oxygen on the n-type conductivity of high-Al-content AlGaN
    Show others...
    2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 13, p. 132113-Article in journal (Refereed) Published
    Abstract [en]

    Issues of major relevance to the n-type conductivity of Al0.77Ga0.23N associated with Si and O incorporation, their shallow donor or deep donor level behavior, and carrier compensation are elucidated by allying (i) study of Si and O incorporation kinetics at high process temperature and low growth rate, and (ii) electron paramagnetic resonance measurements. The Al0.77Ga0.23N composition correlates to that Al content for which a drastic reduction of the conductivity of AlxGa1−xN is commonly reported. We note the incorporation of carbon, the role of which for the transport properties of AlxGa1−xN has not been widely discussed.

    Keywords
    aluminium compounds, electrical conductivity, gallium compounds, III-V semiconductors, impurity states, oxygen, paramagnetic resonance, silicon, wide band gap semiconductors
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-91731 (URN)10.1063/1.4800978 (DOI)000317240200047 ()
    Available from: 2013-04-30 Created: 2013-04-30 Last updated: 2017-12-06Bibliographically approved
    2. Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers
    Open this publication in new window or tab >>Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers
    2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 8, article id 082106Article in journal (Refereed) Published
    Abstract [en]

    This study presents analysis of the residual strain and related surface morphology of high-Al-content Al0.82Ga0.18N layers doped by silicon up to the level of 3×1019 cm-3, and delineates an interplay between  thermodynamic and kinetic processes underlying the epitaxial growth of the layers. It particularly points to the development of certain facet structure (nanopipes) within the doped layers, which is apparent at the high Si doping levels. The formation of nanopipes is considered as a matter of consequence for the performance of the transport properties of the layers. It is anticipated to give rise to facets with SiN-related coverage, outcompeting the  incorporation of Si at substitutional donor sites in the lattice of the Al0.82Ga0.18N layers. We do not find evidence for kinetic stabilization of preferential crystallographic facets when a dopant flow of bis(cyclopentadienyl)magnesium (Cp2Mg), instead of silane (SiH4), is implemented in the doping process.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-106723 (URN)10.1063/1.4894173 (DOI)000342753500035 ()
    Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2018-02-23Bibliographically approved
    3. Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature
    Open this publication in new window or tab >>Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature
    Show others...
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Establishing n- and p- type conductivity via intentional doping in epitaxial layers is fundamental to any semiconductor material system and its relevant device applications. Process parameters such as temperature, precursor gas-flow-rates and pressure may all control intentional doping in metal-organic chemical vapour deposition (MOCVD) of semiconductor materials. The incorporation of impurities such as carbon and oxygen may also be affected by the same process parameters, and the concentration of these impurities has a direct impact on the electrical, optical and thermal properties of epitaxial layers, as has been observed in the MOCVD of technologically-important III-V semiconductor materials such as AlGaAs and GaN.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-106724 (URN)
    Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2014-05-20Bibliographically approved
    4. On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers
    Open this publication in new window or tab >>On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers
    Show others...
    2015 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1306-1310Article in journal (Refereed) Published
    Abstract [en]

    We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for lower Al contents whereas the conductivity drastically reduces for AlGaN layers with Al content in the range x~0.84-1. Degradation of the structural quality and compensation by residual O and C impurities were ruled out as possible explanations for the reduced conductivity. By combining frequency dependent capacitance-voltage and electron paramagnetic resonance measurements we show that the Si donors are electrically active and that the reduced conductivity can be explained by the increased activation energy caused by the sharp deepening of the Si DX state..

    Place, publisher, year, edition, pages
    Wiley-VCH Verlagsgesellschaft, 2015
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-106725 (URN)10.1002/pssb.201451559 (DOI)000355756200016 ()
    Note

    Swedish Research Council (VR); VR Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM); Swedish Energy Agency; Knut and Alice Wallenberg Foundation (KAW); Swedish Governmental Agency for Innovation Systems (VINNOVA)

    Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2017-12-05Bibliographically approved
    5. Mg-doped Al0.85Ga0.15N layers grown by hot-wall MOCVD with low resistivity at room temperature
    Open this publication in new window or tab >>Mg-doped Al0.85Ga0.15N layers grown by hot-wall MOCVD with low resistivity at room temperature
    Show others...
    2010 (English)In: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, ISSN 1862-6254, Vol. 4, no 11, p. 311-313Article in journal (Refereed) Published
    Abstract [en]

    We report on the hot-wall MOCVD growth of Mg-doped AlxGa1-xN layers with an Al content as high as x similar to 0.85. After subjecting the layers to post-growth in-situ annealing in nitrogen in the growth reactor, a room temperature resistivity of 7 k Omega cm was obtained indicating an enhanced p-type conductivity compared to published data for AlxGa1-xN layers with a lower Al content of x similar to 0.70 and a room temperature resistivity of about 10 k Omega cm. It is believed that the enhanced p-type conductivity is a result of reduced compensation by native defects through growth conditions enabled by the distinct hot-wall MOCVD system.

    Place, publisher, year, edition, pages
    John Wiley and Sons, Ltd, 2010
    Keywords
    MOCVD, epitaxy, high-Al-content AlGaN, p-type semiconductors, electrical properties
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-62728 (URN)10.1002/pssr.201004290 (DOI)000284206700005 ()
    Available from: 2010-12-03 Created: 2010-12-03 Last updated: 2014-05-20
    6. High-quality AlN layers grown by hot-wall MOCVD at reduced temperatures
    Open this publication in new window or tab >>High-quality AlN layers grown by hot-wall MOCVD at reduced temperatures
    2012 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 338, no 1, p. 52-56Article in journal (Refereed) Published
    Abstract [en]

    We report on a growth of AlN at reduced temperatures of 1100 C and 1200 C in a horizontal-tube hot-wall metalorganic chemical vapor deposition reactor configured for operation at temperatures of up to 15001600 C and using a joint delivery of precursors. We present a simple route - as viewed in the context of the elaborate multilayer growth approaches with pulsed ammonia supply - for the AlN growth process on SiC substrates at the reduced temperature of 1200 C. The established growth conditions in conjunction with the particular in-situ intervening SiC substrate treatment are considered pertinent to the accomplishment of crystalline, relatively thin, ∼700 nm, single AlN layers of high-quality. The feedback is obtained from surface morphology, cathodoluminescence and secondary ion mass spectrometry characterization.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    A3. Metalorganic chemical vapor deposition; B1. Nitrides; B2. Semiconducting IIIV materials
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-74117 (URN)10.1016/j.jcrysgro.2011.10.052 (DOI)
    Available from: 2012-01-19 Created: 2012-01-19 Last updated: 2017-12-08
    7. Lattice parameters, structural and optical properties of AlN true bulk, homoepitaxial and heteroepitaxial material grown at high temperatures of up to 1400 °C
    Open this publication in new window or tab >>Lattice parameters, structural and optical properties of AlN true bulk, homoepitaxial and heteroepitaxial material grown at high temperatures of up to 1400 °C
    2016 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 17Article in journal (Refereed) Published
    Abstract [en]

    The lattice parameters and residual strain of homo- and heteroepitaxial AlN layers grown at elevated process temperatures (1200-1400 °C) by hot-wall MOCVD are studied. The average lattice parameters for the homoepitaxial AlN layers grown on true bulk AlN substrates are determined to be a = 3.1113 ± 0.0001 Å and c = 4.9808 ± 0.0001 Å are discussed in relation to previously published data. The lattice parameters measured from biaxially strained AlN layers grown on SiC are used to determine the biaxial strain relaxation coefficient to be RB = -0.556 ± 0.021. The structural and optical quality of the heteroepitaxial layers improved with increasing layer thickness and at a thickness of 1.3 μm, crack-free AlN of high crystalline quality with full widths at half maximum of the (0002) and (1012) rocking curves of 25 arc sec and 372 arc sec, respectively, were obtained. Tensile strain developed with increasing layer thickness despite the higher crystalline quality of these layers. This can be explained by the thermal mismatch between the AlN and SiC in combination with island coalescence at the initial stage and/or during the growth.

    Place, publisher, year, edition, pages
    Institute of Physics Publishing (IOPP), 2016
    National Category
    Natural Sciences Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-106726 (URN)10.1088/0022-3727/49/17/175108 (DOI)000374146600013 ()
    Note

    Funding agencies: Swedish Research Council (VR); Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM, VR); Swedish Governmental Agency for Innovation Systems (VINNOVA)

    Vid tiden för disputation förelåg publikationen som manuskript

    Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2017-12-05Bibliographically approved
  • 15.
    Nilsson, Daniel
    et al.
    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.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Lattice parameters, structural and optical properties of AlN true bulk, homoepitaxial and heteroepitaxial material grown at high temperatures of up to 1400 °C2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 17Article in journal (Refereed)
    Abstract [en]

    The lattice parameters and residual strain of homo- and heteroepitaxial AlN layers grown at elevated process temperatures (1200-1400 °C) by hot-wall MOCVD are studied. The average lattice parameters for the homoepitaxial AlN layers grown on true bulk AlN substrates are determined to be a = 3.1113 ± 0.0001 Å and c = 4.9808 ± 0.0001 Å are discussed in relation to previously published data. The lattice parameters measured from biaxially strained AlN layers grown on SiC are used to determine the biaxial strain relaxation coefficient to be RB = -0.556 ± 0.021. The structural and optical quality of the heteroepitaxial layers improved with increasing layer thickness and at a thickness of 1.3 μm, crack-free AlN of high crystalline quality with full widths at half maximum of the (0002) and (1012) rocking curves of 25 arc sec and 372 arc sec, respectively, were obtained. Tensile strain developed with increasing layer thickness despite the higher crystalline quality of these layers. This can be explained by the thermal mismatch between the AlN and SiC in combination with island coalescence at the initial stage and/or during the growth.

  • 16.
    Nilsson, Daniel
    et al.
    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.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 8, article id 082106Article in journal (Refereed)
    Abstract [en]

    This study presents analysis of the residual strain and related surface morphology of high-Al-content Al0.82Ga0.18N layers doped by silicon up to the level of 3×1019 cm-3, and delineates an interplay between  thermodynamic and kinetic processes underlying the epitaxial growth of the layers. It particularly points to the development of certain facet structure (nanopipes) within the doped layers, which is apparent at the high Si doping levels. The formation of nanopipes is considered as a matter of consequence for the performance of the transport properties of the layers. It is anticipated to give rise to facets with SiN-related coverage, outcompeting the  incorporation of Si at substitutional donor sites in the lattice of the Al0.82Ga0.18N layers. We do not find evidence for kinetic stabilization of preferential crystallographic facets when a dopant flow of bis(cyclopentadienyl)magnesium (Cp2Mg), instead of silane (SiH4), is implemented in the doping process.

  • 17.
    Nilsson, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Trinh, Xuan Thang
    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.
    Son, Tien Nguyen
    Linköping University, Department of Physics, Chemistry and Biology. 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.
    On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers2015In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1306-1310Article in journal (Refereed)
    Abstract [en]

    We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for lower Al contents whereas the conductivity drastically reduces for AlGaN layers with Al content in the range x~0.84-1. Degradation of the structural quality and compensation by residual O and C impurities were ruled out as possible explanations for the reduced conductivity. By combining frequency dependent capacitance-voltage and electron paramagnetic resonance measurements we show that the Si donors are electrically active and that the reduced conductivity can be explained by the increased activation energy caused by the sharp deepening of the Si DX state..

  • 18.
    Nilsson, Daniel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Trinh, Xuan Thang
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, Tien Nguyen
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sahonta, S.-L.
    Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK.
    Kappers, M. J.
    Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK.
    Humphreys, C. J.
    Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Establishing n- and p- type conductivity via intentional doping in epitaxial layers is fundamental to any semiconductor material system and its relevant device applications. Process parameters such as temperature, precursor gas-flow-rates and pressure may all control intentional doping in metal-organic chemical vapour deposition (MOCVD) of semiconductor materials. The incorporation of impurities such as carbon and oxygen may also be affected by the same process parameters, and the concentration of these impurities has a direct impact on the electrical, optical and thermal properties of epitaxial layers, as has been observed in the MOCVD of technologically-important III-V semiconductor materials such as AlGaAs and GaN.

  • 19.
    Schoche, S.
    et al.
    University of Nebraska, NE 68588 USA.
    Hofmann, Tino
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. University of Nebraska, NE 68588 USA.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kakanakova-Gueorguie, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kuhne, Philipp
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Lorenz, K.
    University of Lisbon, Portugal.
    Schubert, Mathias
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. University of Nebraska, NE 68588 USA; Leibniz Institute Polymer Research Dresden, Germany.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Infrared dielectric functions, phonon modes, and free-charge carrier properties of high-Al-content AlxGa1-xN alloys determined by mid infrared spectroscopic ellipsometry and optical Hall effect2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 20, article id 205701Article in journal (Refereed)
    Abstract [en]

    We report on the analysis of a combined mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect investigation of wurtzite structure c-plane oriented, crack-free, single crystalline, and high-Al-content AlxGa1-xN layers on 4H-SiC. For high-Al-content AlxGa1-xN, a two mode behavior is observed for both transverse and longitudinal branches of the infrared-active modes with E-1 symmetry, while a single mode behavior is found for the longitudinal modes with A1(LO) symmetry. We report their mode dependencies on the Al content. We determine and discuss static and high frequency dielectric constants depending on x. From the analysis of the optical Hall effect data, we determine the effective mass parameter in high-Al-content AlxGa1-xN alloys and its composition dependence. Within the experimental uncertainty limits, the effective mass parameters are found isotropic, which depend linearly on the Al content. The combination of all data permits the quantification of the free electron density N and mobility parameters mu. Published by AIP Publishing.

  • 20.
    Schoeche, S
    et al.
    University of Nebraska, NE 68588 USA .
    Kuehne, P
    University of Nebraska, NE 68588 USA .
    Hofmann, T
    University of Nebraska, NE 68588 USA .
    Schubert, M
    University of Nebraska, NE 68588 USA .
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Gueorguie, 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.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Electron effective mass in Al0.72Ga0.28N alloys determined by mid-infrared optical Hall effect2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 21, p. 212107-Article in journal (Refereed)
    Abstract [en]

    The effective electron mass parameter in Si-doped Al0.72Ga0.28N is determined to be m* = (0.336 +/- 0.020) m(0) from mid-infrared optical Hall effect measurements. No significant anisotropy of the effective electron mass parameter is found supporting theoretical predictions. Assuming a linear change of the effective electron mass with the Al content in AlGaN alloys and m* = 0.232m(0) for GaN, an average effective electron mass of m* = 0.376m(0) can be extrapolated for AlN. The analysis of mid-infrared spectroscopic ellipsometry measurements further confirms the two phonon mode behavior of the E-1(TO) and one phonon mode behavior of the A(1)(LO) phonon mode in high-Al-content AlGaN alloys as seen in previous Raman scattering studies.

  • 21.
    Trinh, X. T.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, D
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, I. G.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, E
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kakanakova-Georgieva, A
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, N.T.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Negative-U behavior of the Si donor in Al0.77Ga0.23N2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 4, p. 042101-Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance (EPR) spectrum of a shallow donor is observed at low temperatures in darkness in Si-doped Al0.77Ga0.23N epitaxial layers grown on 4H-SiC substrates. It is shown from the temperature dependence of the donor concentration on the neutral donor state measured by EPR that Si is a DX (or negative-U) center but behaves as a shallow donor due to a small separation of only ∼3 meV between the neutral state Ed and the lower-lying negative state EDX. The neutral state is found to follow the effective mass theory with Ed ∼ 52–59 meV.

  • 22.
    Trinh, Xuan Thang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    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.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Son, Nguyen Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Stable and metastable Si negative-U centers in AlGaN and AlN2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 16, p. 162106-1-162106-4Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance studies of Si-doped AlxGa1−xN (0.79 ≤ x ≤ 1.0) reveal two Si negative-U (or DX) centers, which can be separately observed for x ≥ 0.84. We found that for the stable DX center, the energy |EDX| of the negatively charged state DX, which is also considered as the donor activation energy, abruptly increases with Al content for x ∼ 0.83–1.0 approaching ∼240 meV in AlN, whereas EDX remains to be close to the neutral charge state Ed for the metastable DX center (∼11 meV below Ed in AlN).

  • 23.
    Yazdanfar, Milan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kalered, Emil
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Danielsson, Örjan
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Nilsson, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    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, The Institute of Technology.
    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.
    Brominated chemistry for chemical vapor deposition of electronic grade SiC2015In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 3, p. 793-801Article in journal (Refereed)
    Abstract [en]

    Chlorinated chemical vapor deposition (CVD) chemistry for growth of homoepitaxial layers of silicon carbide (SiC) has paved the way for very thick epitaxial layers in short deposition time as well as novel crystal growth processes for SiC. Here, we explore the possibility to also use a brominated chemistry for SiC CVD by using HBr as additive to the standard SiC CVD precursors. We find that brominated chemistry leads to the same high material quality and control of material properties during deposition as chlorinated chemistry and that the growth rate is on average 10 % higher for a brominated chemistry compared to chlorinated chemistry. Brominated and chlorinated SiC CVD also show very similar gas phase chemistries in thermochemical modelling. This study thus argues that brominated chemistry is a strong alternative for SiC CVD since the deposition rate can be increased with preserved material quality. The thermochemical modelling also suggest that the currently used chemical mechanism for halogenated SiC CVD might need to be revised.

1 - 23 of 23
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