Heteroepitaxy and Characterization of Low-Dislocation-Density GaN on Periodically Grooved Substrates
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HETEROEPITAXY AND CHARACTERIZATION OF LOW-DISLOCATION-DENSITY GaN ON PERIODICALLY GROOVED SUBSTRATES T. Detchprohm1, M. Yano2, R. Nakamura2, S. Sano2, S. Mochiduki2, T. Nakamura2, H. Amano1,3, and I. Akasaki1,3 1 High-Tech Research Center, Meijo University 2 Department of Electrical & Electronic Engineering, Meijo University, 3 Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502, Japan ABSTRACT We have developed a new method to prepare low-dislocation-density GaN by using periodically grooved substrates in a conventional MOVPE growth technique. This new approach was demonstrated for GaN grown on periodically grooved α-Al2O3(0001), 6H-SiC(0001)Si and Si(111) substrates. Dislocation densities were 2x107 cm-2 in low-dislocation-density area. INTRODUCTION Growing GaN and related nitride single crystal films on sapphire substrates using low-temperature (LT) buffer layer technique [1] has been significantly contributed to developing optoelectronic and microelectronic devices. However, to further improve the device performance, it is important to reduce dislocation density formed inside the materials. There are several efforts based upon the above technique to gain low-dislocation-density materials such as lateral epitaxial overgrowth [2-3], LT interlayer introduction [4], and mass transport techniques [5]. Demonstrations of characteristics improvement were performed for devices using low-dislocation-density GaN and related materials [6-7]. However, most of the techniques require several processes to be done on GaN single crystal seeds such as a stripe formation of selective-growth masks. Therefore, process damages to GaN seeds, process-induced contaminations and mask-material contaminations become critical factors that affect a quality of subsequently grown GaN layer. To avoid those kind of issues, a newly developed heteroepitaxial technique using a periodically grooved substrate has been proposed and achieved a low-dislocation-density GaN film[8-10]. Since GaN single seeds as well as a selective-growth mask are not necessary, this technology is promising to grow a low-dislocation-density and high-purity GaN single crystal film in a single epitaxy. In this paper, the growth mechanism and residual strain comparison were discussed. EXPERIMENT Periodically grooved (PG) substrates of basal plane sapphire, Si(111) and 6H-SiC (0001) were used for heteroepitaxy of GaN single crystal in metal organic vapor phase epitaxy (MOVPE) method. Width of a single groove was approximately 5 µm with a 10 µm interval. The substrates -
with stripes which were parallel to direction of GaN were used. Prior to a growth, a substrate was thoroughly cleaned up by organic solvents and acids to minimize any possible process contaminations. A deposition of nucleation layer and GaN were performed in an atmospheric MOVPE reactor with TMGa-TMAl-NH3-H2 gas system. An nucleation layer of LT-AlN was deposited on a PG-sapphire substrate, while a thin single crystalline AlGaN film was grown on a
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