Growth and Characterization of InGaN/GaN Heterostructures Using Plasma-Assisted Molecular Beam Epitaxy
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Gap Semiconductor Team, Microelectronics Technology Laboratory, Electronics and Telecommunications Research Institute 161 Kajung-Dong, Yusong-Gu, Taejon, Korea 305-350
Research
Structural and optical properties of In0.2Ga 0.8N/GaN heterostructures grown by plasma-assisted molecular beam epitaxy have been investigated as a function of rf plasma power. Indium incorporation resulted in the higher rf power level suppressing 3D island growth with reduced introduction of defects in In0 .2Ga 0 8N in comparison with GaN. Sharp morphology at interfaces and strong transitions in photoluminescence reveal the optimum rf power around 400 W in our experimental set up for the growth of In0.2Ga 0.8N/GaN heterostructures. Our experimental observations suggest that the presence of indium on surface modulates the rate of plasma stimulated desorption and diffusion, and reduces the formation of damaged subsurface. INTRODUCTION Recently, lots of achievements have been accomplished in the field of GaNbased nitride semiconductors by remarkable breakthroughs in epitaxial growth technology [1]. Plasma assisted molecular beam epitaxy (PAMBE) has demonstrated useful results along with its advantageous features such as low temperature processes and atomic layer growth. However, the development of GaN-based epilayers using PAMBE has been hindered by uncertainty about the effect of the plasma parameters on film quality and inadequate control of the energetic species in the nitrogen plasma. Meanwhile, the application of very low energy ion beams of a few tens of eV have focused on the modulation of surface reaction kinetics, strain relaxation, and island formation [2,3]. Despite the relevant role of plasma parameters, relatively few articles have focused on the study of plasma parameters in GaN epilayers using PAMBE [4,5]. A fundamental understanding of the interactions of energetic particles with the surface of GaN-based epi layers would enable the tradeoff between damage production and surface enhancement. The objective of this study is to understand the effect of the rf power on the
383 Mat. Res. Soc. Symp. Proc. Vol. 572 ©1999 Materials Research Society
growth of GaN-based epilayers by exploring correlations between the structural/optical properties and the rf plasma power. Our experimental results on In0.2Gao.N/GaN 8 superlattice (SL) structures provide a framework for understanding the complicated role of plasma parameters on the growth of GaN-based heterostructures. EXPERIMENT GaN-based heterostructures were grown using PAMBE equipped with an inductively coupled rf plasma source (SVT Associates) [6]. After the conventional solvent cleaning and etching processes, 20-nm-thick AIN buffer layers were grown on sapphire (0001) at 500 0C. Then GaN epilayers were grown at 720'C and followed by the growth of ten periods of In0 2Ga 08N/GaN(25/50A) at 670'C. The thickness of InGaN was designed to be smaller than the critical thickness, 7.6 nm, estimated from a Matthew and Blakeslee model. The growth chamber maintained 7x1 0-5 torr for whole grow
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