GaN Epitaxial Growth Process at High Growth Temperature by NH 3 Source Molecular Beam Epitaxy
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GaN Epitaxial Growth Process at High Growth Temperature by NH3 Source Molecular Beam Epitaxy Naoki Ohshima*, Akihiro Sugihara, Naoya Yoshida and Naohiko Okabe Dept. of Advanced Materials Sci. & Eng., Faculty of Eng., Yamaguchi University, 2-16-1, Tokiwa-dai, Ube, Yamaguchi 755-8611, Japan
ABSTRACT We have investigated in detail dependence of annealing GaN buffer layer and GaN growth processes on a sapphire substrate at a high temperature of 1000 degree C. The GaN layers are grown by NH3 gas source molecular beam epitaxy. The behavior of GaN buffer and epitaxial layer has been observed by in-situ reflection high-energy electron diffraction and the surface morphologies of as-grown and chemically etched GaN layers by atomic force microscopy. It is found that there is distinct difference in the surface morphology of epitaxial GaN layer between at growth temperatures of below 950 degree C and that of 1000 degree C. It has been considered that the growth kinetics of GaN epitaxial layer extremely depends on the growth temperature.
INTRODUCTION The GaN and related compounds are promising materials for blue and short wavelength optoelectronic devices [1-4]. Many GaN-based applications of optoelectronic device are demonstrated on sapphire substrate because sapphire substrate has advantages such as the thermal stability and inactivity for nitridation. However, it is hard to obtain the high-quality GaN on a sapphire substrate with low density of threading dislocation because of the large misfit of lattice constants and the difference of thermal coefficients between GaN epilayer and sapphire substrate [5-14]. It is essential for realization of the ideal GaN epitaxial layer to study the initial anneal and growth processes of GaN epitaxial layer at a high growth temperature of 1000 degree C. There has been little work on the in-situ investigation of annealing and growth processes of GaN at high temperatures using NH3 gas source molecular beam epitaxy (GS-MBE) [15, 16]. In the present work, we have investigated the thermal annealing and initial growth process of GaN buffer and epitaxial layer on sapphire substrate using NH3 GS-MBE with in-situ reflection high-energy electron diffraction (RHEED). And also the surface morphology of etched GaN layers by an aqueous solution of NaOH has been studied by ex-situ atomic force microscopy (AFM) observations. EXPERIMENTAL DETAILS Growth apparatus and sequence Figure 1(a) shows a schematic diagram of growth apparatus equipment with an in-situ RHEED system. A growth chamber was evacuated by twin turbo molecular vacuum pumps mounted in parallel, and the base pressure was of 1×10-10 Torr. Figure 1(b) shows schematic
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diagram of changing of substrate temperatures along an experimental time sequence. GaN have been grown by using of a GS-MBE apparatus with an in-situ RHEED system. Since details of apparatus equipment have been reported previously [9], only a brief outline is described here. A growth chamber was evacuated by a molecular vacuum pump, and the base pressure was 1×
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