Microstructures of GaN and In x Ga 1-x N Films Grown by MOCVD on freestanding GaN Templates
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Microstructures of GaN and InxGa1-xN Films Grown by MOCVD on freestanding GaN Templates J. Jasinski, Z. Liliental-Weber, D. Huang1, M. A. Reshchikov1, F. Yun1, H. Morkoç1, C. Sone2, S. S. Park2 and K. Y. Lee2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 1 Virginia Commonwealth University, Richmond, VA, USA 2 Samsung Advanced Institute of Technology, P.O.Box 111, Suwon, KOREA ABSTRACT We summarize structural properties of thick HVPE GaN templates from the point of view of their application as substrates for growth of nitride layers. This is followed by the results of optical and structural studies, mostly transmission electron microscopy, of nitride layers grown by MOCVD on top of the HVPE substrates. The results indicate high structural quality of these layers with a low density of threading dislocations (in the range of 106 cm-2). Convergent beam electron diffraction studies showed that the MOCVD GaN films have Ga-polarity, the same polarity as the HVPE GaN substrates. Structural studies of an InGaN layer grown on top of the MOCVD GaN film showed the presence of two layers, which differed in lattice parameter and composition. The upper layer, on the top of the structure had a clattice parameter about 2 % larger than that of GaN and contained 10.3 ± 0.8 % of In. Values measured for the thinner, intermediate layer adjacent to the GaN layer were about 2.5 times lower.
INTRODUCTION Large area substrates for homoepitaxial growth of GaN layers have recently became available as a result of recent progress in production of thick freestanding GaN layers grown by hydride vapor phase epitaxy (HVPE) [1,2] followed by laser-assisted liftoff [3-6]. Such substrates have been successfully applied to grow GaN layers using both, metal organic chemical vapor deposition (MOCVD) [4,7] and molecular beam epitaxy (MBE) [8] methods, resulting in high quality films, as demonstrated by the high quality of their optical spectra and good electrical characteristics. In this paper we report results of structural studies obtained by transmission electron microscopy (TEM), x-ray diffraction (XRD), and photoluminescence (PL) of such GaN and InxGa1-xN films grown by MOCVD on freestanding HVPE GaN substrates. Fabrication of high quality InxGa1-xN/GaN heterostructures is important because such heterostructures are used as active layers in nitride based light emitting devices. Although bright light emitting devices, and lasers from the visible to the ultraviolet region have been fabricated, the growth of high quality InxGa1-xN films and their microstructures are still not well understood. Application of high quality freestanding GaN substrates for fabrication of InxGa1-xN/GaN heterostructure eliminates the negative effects resulting from severe lattice mismatch associated with heteroepitaxy on sapphire, SiC and other foreign substrates. The paper is divided into two parts. First, the microstructure and structural characteristics of HVPE GaN will be discussed. The properties of both, thin HVPE GaN layers,
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