Epitaxial Growth of AlN on 6H-SiC (1120) by Molecular-Beam Epitaxy and Effect of Low-Temperature Buffer Layer
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Epitaxial Growth of AlN on 6H-SiC (1120) by Molecular-Beam Epitaxy and Effect of Low-Temperature Buffer Layer N. Onojima, J. Suda and H. Matsunami Department of Electronic Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan ABSTRACT Aluminum nitride (AlN) has been grown on 6H-silicon carbide (SiC) substrates with the IJ non-polar (1120) face using rf plasma-assisted molecular-beam epitaxy (rf-MBE). Reflection IJ high-energy electron diffraction (RHEED) revealed that AlN and 6H-SiC (1120) had an exact IJ IJ epitaxial relationship, i.e., [112 0]AlN||[112 0]SiC and [0001]AlN||[0001]SiC. From the result of microscopic Raman scattering spectroscopy, the stacking structure of the AlN epitaxial layer was suggested to be a 2H structure, not a 6H structure. A directly grown AlN layer and layer with AlN low-temperature (LT) buffer layer were investigated based on atomic force microscopy (AFM) and X-ray diffraction (XRD). INTRODUCTION AlN/SiC structures are of current importance for the development of high-temperature electronic devices. In most cases, epitaxial growth of AlN on SiC is carried out on commercially available on- or off-axis (0001) substrates and extensive studies of the growth mechanism and crystalline structure are performed [1,2]. IJ Recently, SiC substrates with the non-polar (1120) face are shipped from some companies. Exploring a new crystal face is very important to expand the design of the device structure and to develop new functional devices. In addition, to investigate the growth and structure of AlN on a non-polar SiC substrate is scientifically interesting. IJ In this study, AlN growth on 6H-SiC (11 2 0) substrates has been performed by rf plasma-assisted molecular-beam epitaxy (rf-MBE). AlN epitaxial layers were investigated by in situ reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray diffraction (XRD) and microscopic Raman scattering spectroscopy. The epitaxial IJ relationship between AlN and 6H-SiC (1120) and the polytype of the AlN layer were examined. A direct growth and two-step growth using an AlN low-temperature (LT) buffer layer were comparatively studied.
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The substrates used in this study were 6H-SiC wafers with the (1120)-vicinal face from Nippon Steel Corporation. AlN epitaxial layers were grown in an MBE chamber equipped with a standard effusion cell for Al evaporation and an EPI Unibulb rf plasma cell for producing active nitrogen (N*). The substrate was thermally cleaned at 1000°C for 30 min in an ultrahigh vacuum of 10-9 Torr, and then an AlN layer was directly grown at 1000°C. Details of the growth condition were reported in [3]. In a two-step growth, a 20-nm-thick AlN LT buffer layer was grown at 600°C prior to the 1000°C -growth mentioned above. The total thickness of AlN layers ranged from 0.4 to 1.0 µm. DISCUSSION IJ
Figure 1(a) shows the RHEED pattern of a 6H-SiC (1120) substrate with the [0001] azimuth. At the initial stage of the direct growth, a spotty pattern of AlN was obs
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