Reduction of defects in RF-MBE grown GaN on sapphire by optimization of nitridation temperature and intermediate layer parameters

Despite intense research efforts into the development of GaN and AlN substrates, sapphire remains a popular substrate choice for III-N-based epitaxy of electronic and optoelectronic devices. With sapphire substrates, certain pre-growth procedures are used to wet the substrate surface and accommodate the high lattice mismatch between III-nitrides and Al/sub 2/O/sub 3/. These initial steps taken to initiate film growth by MBE, such as the nitridation of the sapphire surface to form AlN and the following deposition of buffer layers, play a critical role in determining epilayer properties.