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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.
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.
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.