Either step-flow or layer-by-layer growth for AIN on SiC (0001) substrates
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Either step-flow or layer-by-layer growth for AlN on SiC (0001) substrates Jun Suda1,2, Norio Onojima2, Tsunenobu Kimoto2 and Hiroyuki Matsunami2 1 PRESTO “Nanostructure and Material Property”, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan 2 Department of Electronic Science and Engineering, Kyoto University, Kyoto University Katsura Campus, Nishikyo-ku, Kyoto 616-8510, Japan ABSTRACT AlN was grown on 4H- or 6H-SiC (0001) on-axis substrates by plasma-assisted molecular beam epitaxy. By utilizing optimized SiC surface pretreatment, RHEED oscillations just after the growth of AlN were obtained with high reproducibility. This study focused on the growth kinetics of AlN and the correlation between kinetics and the crystalline quality of the grown layers. It was found that the growth mode changed from layer-by-layer to step-flow for high growth temperatures, while for lower temperatures the layer-by-layer growth mode persisted. The mechanism responsible for the change in growth mode is discussed. Symmetrical (0002) and asymmetrical (01-14) x-ray rocking curve measurements were carried out to evaluate the crystalline quality. For the (0002) peak, both high-temperature and low-temperature grown layers showed almost the same FWHM values. On the other hand, for the (01-14) peak, the FWHM of low-temperature grown AlN was much smaller (180 arcsec) than that of the high-temperature grown AlN (450 arcsec). INTRODUCTION Growth of high-quality AlN on SiC is a key issue to realize high-performance electronic devices such as GaN-based high-power high-frequency heterojunction field-effect transistors (HFETs) or AlN/SiC metal-insulator-semiconductor FETs (MISFETs). We have investigated precise control of the SiC (0001) surface and optimization of AlN growth conditions in molecular-beam epitaxy (MBE) [1]. Recently, we have realized RHEED intensity oscillations just after the growth of AlN on SiC with high reproducibility [2]. In this study, we focused on the growth kinetics of AlN and the correlation between kinetics and the crystalline quality of the grown layers.
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EXPERIMENTAL The substrates used in this study were commercially available on-axis 4H- and 6H-SiC(0001)Si wafers (unintentional off angle ~ 0.2°). The substrates were first degreased using conventional organic solvents and dipped in HCl, HCl+HNO3 (3:1) and HF solutions, and then loaded into a SiC chemical vapor deposition (CVD) system for HCl-gas etching. The HCl-gas etching was carried out at 1300°C for 10 min under a gas flow of HCl (3 sccm) diluted with H2 carrier gas (1 slm). The details of HCl-gas etching have been reported by Nakamura et al.[3] The gas etching procedure successfully removes the polishing scratches typically present on the surfaces of as-received wafers, resulting in an atomically flat terrace structure with a 4 (or 6) monolayer (ML)-height step. Since the atomic stacking of AlN (2H, wurtzite) is different from that of SiC (4H or 6H), formation of steps of unit cell height in the SiC substrate is v
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