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Electrical and luminescent properties and deep traps spectra of N-polar GaN films
Polyakov, A.Y.,Smirnov, N.B.,Govorkov, A.V.,Sun, Q.,Zhang, Y.,Cho, Y.S.,Lee, I.H.,Han, J. Elsevier 2010 Materials science and engineering B. Advanced Func Vol.166 No.1
Electrical and luminescent properties of N-polar undoped GaN films grown using low temperature GaN buffers on on-axis and miscut sapphire and on-axis AlN buffers are compared to the properties of Ga-polar films grown on low temperature GaN buffers. It is shown that the concentration of residual donors increases by about an order of magnitude for on-axis N-polar growth and by two orders of magnitude for off-axis growth compared to Ga-polar films. On-axis films for both Ga-polar and N-polar polarities show the presence of n<SUP>+</SUP> interfacial layers greatly influencing the apparent electron concentration and mobility deduced from capacitance-voltage C-V measurements. These interfacial layers are much less prominent in the miscut N-polar films. Growth on N-polar greatly increases the concentration of electron traps with activation energy of 0.9eV possibly related to Ga-interstitials.
Deep hole traps in undoped n-GaN films grown by hydride vapor phase epitaxy
Lee, In-Hwan,Polyakov, A. Y.,Smirnov, N. B.,Govorkov, A. V.,Usikov, A. S.,Helava, H.,Makarov, Yu. N.,Pearton, S. J. American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.115 No.22
Deep hole traps were studied in bulk free-standing GaN crystals and in thinner (10-20 mu m) GaN films prepared by hydride vapor phase epitaxy (HVPE) on sapphire. Six hole traps in different combinations were detected in these crystals, H1 (activation energy 0.92-0.94 eV), H2 (0.55 eV), H3 (0.65-0.7 eV), H4 (0.85-0.9 eV), H5 (1.1-1.2 eV), and H6 (0.95-1.05 eV). The dominant traps in all samples were the H5 and H6 traps that were attributed, respectively, to gallium vacancy complexes with oxygen (V-Ga-O) and substitutional carbon related centers. We associate the H5 hole traps with the red luminescence bands, the H4 hole traps with the green luminescence bands, and the H6 hole traps with the yellow luminescence bands often observed in HVPE GaN. These attributions are based on the low energy thresholds of the deep traps optical excitation spectra and the depth of the respective trap levels. (C) 2014 AIP Publishing LLC.
Electrical properties and radiation detector performance of free-standing bulk n-GaN
Lee, I.-H.,Polyakov, A.Y.,Smirnov, N.B.,Govorkov, A.V.,Kozhukhova, E.A.,Zaletin, V.M.,Gazizov, I.M.,Kolin, N.G.,Pearton, S.J. American Vacuum Society 2012 Journal of vacuum science and technology. material Vol.30 No.2
Effects of laterally overgrown n-GaN thickness on defect and deep level concentrations
Polyakov, A. Y.,Smirnov, N. B.,Govorkov, A. V.,Markov, A. V.,Yakimov, E. B.,Vergeles, P. S.,Lee, In-Hwan,Lee, Cheul Ro,Pearton, S. J. American Vacuum Society 2008 JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B - Vol.26 No.3
Quantum Barrier Growth Temperature Affects Deep Traps Spectra of InGaN Blue Light Emitting Diodes
Polyakov, A. Y.,Smirnov, N. B.,Shchemerov, I. V.,Yakimov, E. B.,Yakimov, E. E.,Kim, Kyu Cheol,Lee, In-Hwan The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.5
<P>Electroluminescence (EL) efficiency, deep electron and hole traps spectra, microcathodoluminescence (MCL), electron beam induced current (EBIC) imaging, and MCL spectra were studied for blue GaN/InGaN multi-quantum-well (MQW) light emitting diodes differing by the temperature at which the GaN barriers of the MQW active region were grown. It was found that increasing the growth temperature from 850 to 920 degrees C very strongly suppressed the formation of deep electron traps with level at E-c-1 eV in the GaN barriers and of the hole traps with levels at E-v+0.7eV in InGaN QWs. The suppression of the formation of the E-c-1 eV electron trap, a known prominent nonradiative recombination center in n-GaN, improved the carrier injection efficiency into the InGaN QWs and increased the external quantum efficiency by about 9%. EBIC and MCL imaging showed that the density of threading dislocations and terminating them V-pits was relatively low and similar for both studied growth temperatures, close to 10(8) cm(-2) . The cross-sectional dimensions of the V-pits were measurably higher for increased growth temperature. However, the rather low dislocation density and rather high dimensions of the V-pits were believed to result in minor contribution of these defects to the observed EL efficiency changes. (C) 2018 The Electrochemical Society.</P>
Polyakov, A. Y.,Jang, Lee-Woon,Smirnov, N. B.,Govorkov, A. V.,Kozhukhova, E. A.,Yugova, T. G.,Reznik, V. Y.,Pearton, S. J.,Baik, Kwang Hyeon,Hwang, Sung-Min,Jung, Sukkoo,Lee, In-Hwan American Institute of Physics 2011 JOURNAL OF APPLIED PHYSICS - Vol.110 No.9
<P>The electrical properties, presence of deep electron and hole traps and photoluminescence spectra were measured for undoped a-GaN films grown by metal-organic chemical vapor deposition (MOCVD) in a two-stage process using a high V/III ratio at the first stage and low V/III ratio at the second stage. Growth was performed on r-sapphire substrates with a high temperature GaN nucleation layer. The films showed a full width at half maximum of 450-470 arcseconds for the (11-20) x-ray rocking curve with little anisotropy with respect to the sample rotation around the growth direction. The stacking fault (SF) density determined by selective etching was similar to 5 x 10(4) cm(-1). The residual donor concentration was 10(14)-10(15) cm(-3), with a very low density (2.5 x 10(13) cm(-3)) of electron traps located at E-c - 0.6 eV, which are believed to be one of the major non-radiative recombination centers in nonpolar GaN. Consequently, the films showed a high intensity of bandedge luminescence with negligible contribution from defect bands associated with SFs. In contrast to previously studied nonpolar GaN films, the a-GaN layers showed a high concentration of gallium-vacancy-related acceptors near E-v + 1 eV and a strong yellow luminescence band, both indicating that growth conditions were effectively N-rich. a-AlGaN/GaN heterojunctions with thin heavily Si doped AlGaN barriers made on a-GaN substrates showed two-dimensional electron gas (2DEG) concentrations of 1.2 x 10(13) cm(-3), with 2DEG mobility of 80 cm(2)/Vs. Capacitance-voltage profiling of Schottky diodes on these HJs suggest that the 2DEG is fully depleted by the built-in voltage of the Schottky diode. (C)2011 American Institute of Physics. [doi: 10.1063/1.3658026]</P>