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E2.9.1

Metalorganic Chemical Vapor Deposition of Non-polar III-Nitride Films over a-plane SiC Substrates Jiawei Li, Zheng Gong, Changqing Chen, Vinod Adivarahan, Mikhail Gaevski, Edmundas Kuokstis, Maxim Shatalov, Ying Gao, Zehong Zhang, Arul Arjunan, T. S. Sudarshan, H. Paul Maruska, Jinwei Yang and M. Asif Khan Department of Electrical Engineering, University of South Carolina, Columbia, South Carolina 29208, U.S.A. ABSTRACT We report progress in growing non-polar a-plane III-nitride films and heterostructures over a-plane 4H-SiC. a-plane SiC is more closely lattice-matched to a-plane GaN than is r-plane sapphire. Consequently, better structural quality a-plane nitride films may result over a-plane SiC substrates. By migration enhanced metalorganic chemical vapor deposition (MEMOCVD), an atomically smooth (112 0) AlN layer with RMS roughness of 0.3nm was obtained. From the results of XRD, the structural defects in the AlN layer on SiC substrates were strongly reduced compared to those grown on r-plane sapphire. Also by applying our selective area lateral epitaxy (SALE) growth procedure, we achieved high structural and optical quality a-plane GaN films on 4H-SiC with RMS roughness only 0.4nm. Therefore, non-polar III-nitride films and heterostructures on SiC substrates are promising building blocks for realizing high performance polarization-free devices. INTRODUCTION At present, basically all functional GaN-based devices are being deposited on either (0001) sapphire or (0001) SiC substrates. However, III-nitride films grown with nonpolar orientations such as [ 1120 ] or [ 1 1 00 ] can be very attractive for light emitting devices since multiple quantum wells formed on non-polar faces avoid the permanent electric dipole which exists along the c-axis, and hence are not deleteriously influenced by the quantum-confined Stark effect.1 This internal electric field associated with the polar [0001] orientation leads to spatially indirect optical transitions for UV-emitting LEDs, which severely reduces the emission efficiency.2 Also, high electron mobility transistors on non-polar planes are especially interesting because of the possibility to modulate the sheet carrier density by extrinsic doping. Recently, several groups have reported the epitaxial growth of non-polar (112 0) nitride films on (1 1 02) r-sapphire substrates.3,4,5,6 However, the crystalline quality of GaN (112 0) layers grown on sapphire is typically found to be inferior to that of GaN (0001) layers, even though the lattice mismatch in the direction of the GaN c-axis is only 1.1%.7 According to work by Elwell et al using bulk GaN crystal grown in liquid gallium, only the {0001} , {1010} , {1011} , and {1012} facets are stable under equilibrium conditions, which may explain the poor surfaces usually encountered with a-plane GaN.8 Such nitride films have high densities of basal plane stacking faults and threading dislocations, which deteriorate the

E2.9.2

performance of devices fabricated on material with this non-polar orientation.9 Hence we have undert