For obtaining excellent epitaxial wafers with low sheet resistance and smooth surface, which are essential for higher power AlGaN/GaN high electron mobility transistor (HEMT), we adopted the combination of GaN/AlN-superlattic (SL) quasi-AlGaN alloy barrier, whose preparation is more suitable for MBE technique, and precisely-controlled vicinal substrates of SiC. It was found that the crystalline quality of the GaN channel layer was improved due to the vicinal substrates with the vicinal angle up to 2 degrees. Furthermore, by the effect of SL quasi alloy barrier, the surface of the HEMT structures exhibited step flow feature with the rms of the surface roughness 0.31 nm, although the equivalent composition of the SL quasi alloy barrier was as high as 0.5. In consequence of the improvement of the crystalline quality and the high At content, the sheet resistance of 320 ohm/square was obtained. (c) 2007 Elsevier B.V. All rights reserved.