Characterization of a-plane AlGaN/GaN heterostructure grown on r-plane sapphire substrate
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0892-FF07-08-EE05-08.1
Characterization of a-Plane AlGaN/GaN Heterostructure Grown on r-Plane Sapphire Substrate M. Iwaya, Y. Okadome, Y. Tsuchiya, D. Iida, A. Miura, H. Furukawa, A. Honshio, Y. Miyake, S. Kamiyama, H. Amano and I. Akasaki Faculty of Science and Technology, 21st COE program ”Nano-Factory”, Meijo University, 1-501, Tempaku-ku, Nagoya 468-8502, Japan ABSTRACT The anisotropically biaxial strain in a-plane AlGaN on GaN is investigated by X-ray diffraction analysis of the heterostructure of AlGaN and GaN grown on r-plane sapphire. The AlGaN layer with a low AlN molar fraction or small thickness is coherently grown on the GaN layer both along the m-axis and c-axis. An increase in AlN molar fraction or thickness in AlGaN, results in a slight relaxation of AlGaN only in one direction due to tensile stress along the c-axis, which is caused by the underlying GaN layer during the growth. The cause of the relaxation of AlGaN in one direction is thought to be a large anisotropically biaxial stress. 1. INTRODUCTION Recently, the high performance violet, blue and green light emitting diodes (LEDs) and violet laser diodes (LDs) using c-plane group III nitrides have been commercialized and widely used all over the globe. They have been developed as a result of outstanding breakthroughs such as the improvement in crystalline quality using a low-temperature-deposited buffer layer [1] and the realization of the conductivity control of nitrides [2-4]. However, the performance of these LEDs in longer wavelength regions, such as the blue and green regions, is still insufficient. The strong internal electric field perpendicular [5] to the heterointerfaces of the quantum wells is thought to be the major obstacle for achieving high-efficiency green or longer-wavelength LEDs. The use of nonpolar a-plane nitrides potentially solves this problem [6]. Therefore, the growth of GaN on r-plane sapphire, which results in a-plane GaN, has attracted considerable attention. The characterization of multiple quantum wells [7,8] and the performance of LEDs [9] have already been reported. To fabricate high-performance nitride-based devices such as LEDs, LDs and field-effect transistors, the hetero epitaxial growth of AlGaN ternary alloy on GaN (AlGaN/GaN) is indispensable. In the hetero-epitaxial growth of c-plane AlGaN/GaN, the AlGaN ternary alloy can be grown coherently on binary GaN, which means that the AlGaN films are under isotropically biaxial tensile stress [9]. Moreover, heterostructural c-plane nitride was characterized in a-plane AlGaN/GaN [10]. However, for heteroepitaxial a-plane nitride, it is not suitable to use the same characterization because of the anisotropically biaxial stress in films.
0892-FF07-08-EE05-08.2
In this study, the strain in an a-plane AlGaN/GaN heterostructure was characterized using X-ray diffraction (XRD) analysis. Moreover, we discussed the mechanism of the relaxation in anisotropically biaxial strain in < 1120 > a-plane nitrides.
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AlGaN (50nm)
2. EXPERIMENTS An a-plane AlGaN/GaN heterostructur
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