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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.,Jeon, D.W.,Govorkov, A.V.,Smirnov, N.B.,Sokolov, V.N.,Kozhukhova, E.A.,Yakimov, E.B.,Lee, I.H. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.554 No.-
Nanopillar structures were prepared by dry etching of maskless epitaxial lateral overgrowth (MELO) GaN samples using a mask of Ni nanoparticles formed upon annealing thin Ni films deposited on top of SiO<SUB>2</SUB>/GaN. Under our experimental conditions the average nanopillars dimensions were close to 170nm, with the nanopillars density close to 10<SUP>9</SUP>cm<SUP>-2</SUP>. The nanopillars formation was random and not correlated with the threading dislocation density in MELO GaN, as evidenced by comparing the size and density of nanopillars in the wing and seed regions of MELO GaN differing in dislocation density by an order of magnitude. After dry etching the luminescent intensity of nanopillars became actually lower than the intensity from the unetched matrix due to the impact of defects introduced in the sidewalls during nanopillars formation. The intensity greatly increased, together with a decrease in the leakage current of Schottky diodes, after rapid thermal annealing of nanopillar structures at 900<SUP>o</SUP>C and further increased after additional etching in KOH solution. These changes are attributed to annealing of radiation defects introduced by dry etching and further removal of the damaged region by KOH etching. The results suggest that, in nanopillar structures produced by dry etching, some increase of internal quantum efficiency alongside improvement of light extraction efficiency are responsible for the observed luminescence intensity changes.
Deep traps and enhanced photoluminescence efficiency in nonpolar a-GaN/InGaN quantum well structures
Polyakov, A. Y.,Jang, Lee-Woon,Jo, Dong-Seob,Lee, In-Hwan,Smirnov, N. B.,Govorkov, A. V.,Kozhukhova, E. A.,Hyeon Baik, Kwang,Hwang, Sung-Min American Institute of Physics 2012 JOURNAL OF APPLIED PHYSICS - Vol.111 No.3
Polyakov, I.V.,Bolton, R.,Greve, R.,Hutchings, J.,Kim, S.J.,Kim, Y.,Lee, S.H.,Ohata, T.,Saito, F.,Sugimoto, A.,Suzuki, R. Elsevier Science 2014 Polar science Vol.8 No.2
Rapid and dramatic climate changes in the Arctic and the projection of their impacts on lower-latitude regions require careful evaluation, understanding, and use of multidisciplinary, internationally coordinated efforts. The Third International Symposium on Arctic Research (ISAR-3), devoted to these objectives, was held on January 14-17, 2013 in Tokyo, and was an essential step in this direction. The pool of papers that make up this Special Issue provides an insight into the discussions conducted during the ISAR-3 meeting.
Electrical properties and deep traps spectra of a-plane GaN films grown on r-plane sapphire
Polyakov, A.Y.,Smirnov, N.B.,Govorkov, A.V.,Markov, A.V.,Sun, Q.,Zhang, Y.,Yerino, C.D.,Ko, T.S.,Lee, I.H.,Han, J. Elsevier 2010 Materials science & engineering. B, Advanced funct Vol.166 No.3
Electrical properties, deep traps spectra and luminescence spectra were studied for two undoped a-plane GaN (a-GaN) films grown on r-plane sapphire using metalorganic chemical vapor deposition and differing by structural perfection. For sample A, the a-GaN film was directly deposited on AlN buffer. A two-step growth scheme was implemented for sample B, including an initial islanding growth stage and a subsequent enhanced lateral growth. Preliminary detailed X-ray analysis showed that the stacking faults density was 8x10<SUP>5</SUP>cm<SUP>-1</SUP> for sample A and 1.7x10<SUP>5</SUP>cm<SUP>-1</SUP> for sample B. Electrical properties of a-GaN films were largely determined by deep traps with a level near E<SUB>c</SUB> -0.6eV, with other prominent traps having the activation energy of 0.25eV. The Fermi level was pinned by the E<SUB>c</SUB> -0.6eV deep traps for sample A, but shifted to the vicinity of the shallower 0.25eV traps for sample B, most likely due to the reduced density of the 0.6eV traps. This decrease of deep traps density is accompanied by a very pronounced improvement in the overall luminescence intensity. A correlation of the observed improvement in deep traps spectra and luminescence efficiency with the improved crystalline quality of the films is discussed.