GaN Growth on Si Using ZnO Buffer Layer
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GaN Growth on Si Using ZnO Buffer Layer K.C. Kim, S.W. Kang, O. Kryliouk and T.J. Anderson Department of Chemical Engineering, P.O. Box 116005, Gainesville, FL 32611-6005 D. Craciun National Institute for Laser, Plasma and Radiation, Romania V. Craciun, R.K. Singh Materials Sciences and Engineering, P.O. Box 116400, Gainesville, FL 32611-6400
ABSTRACT ZnO films were deposited by Pulsed Laser Deposition (PLD) onto silicon substrates to serve as a buffer layer for GaN films grown by MOCVD. A ZnO buffer layer was found to improve the quality of GaN grown on Si. The thermal stability of ZnO as a buffer layer was also examined. It was determined that exposure of ZnO/Si to NH3 at high temperature (> 600 o C) results in the decomposition of ZnO and subsequent poor nucleation of GaN. The ZnO layer thickness on GaN quality was found to be important. INTRODUCTION It is well documented that the column III-nitride semiconductors have considerable potential for use in displays, optical data storages, reprographics, high power, high frequency electronic devices, UV detectors, and related technologies [1,2]. The lack of a suitable substrate, however, has hindered the growth of high quality GaN films. Although the favored substrate for GaN growth is (0001) sapphire, it has limitations including a large lattice mismatch with GaN and the accompanying significant bowing at large diameters, high electrical resistivity, and lack of suitable cleavage planes. The Si substrates for GaN growth is attractive given its low cost, large diameter, high crystal and surface quality, controllable electrical conductivity, and high thermal conductivity. In addition, the use of Si wafers promises easy integration of GaN based optoelectronic devices with Si based electronic devices [3]. Indeed, GaN-based devices have been demonstrated on Si [4]. The direct growth of GaN on Si, however, resulted in substantial diffusion of Si into the GaN film, relatively high dislocation density (~1010cm-2) [5] and cracking of the GaN film [6]. GaN is also known to poorly nucleate on Si substrate, leading to an island-like GaN structure and poor surface morphology [6]. In this study, a ZnO buffer layer was evaluated as a buffer layer for GaN growth on Si. ZnO has previously been tested as a buffer layer for Hydride Vapor Phase Epitaxy (HVPE) growth of GaN on sapphire [7-10]. GaN growth on ZnO/Si structures has also been reported [11-12]. In general, the use of a ZnO buffer layer produced good quality GaN on both Si and sapphire substrates [7-12], even though ZnO is known to be thermally unstable at the high growth temperature of GaN. For ZnO/Si, no continuous two-dimensional GaN layer could be obtained without first growing a low temperature GaN buffer layer to prevent the thermal decomposition of ZnO [11]. HVPE grown GaN films on ZnO/sapphire without this low temperature GaN buffer layer exhibited cracks and peeling when thick (200 nm) ZnO buffer layer were grown [7]. It was suggested that the thermal decomposition of ZnO led to the
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growth of poor q
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