GaN Grown on Sputtering AlN Buffer Layer with Sapphire Substrate by Plasma-Assisted Molecular-Beam Epitaxy

The non-polar gallium nitride (GaN) film is a potential candidate for high-efficient optoelectronic devices. This study reports the characterization of GaN grown on aluminum nitride (AlN) buffer layer by plasma-assisted molecular-beam epitaxy (PA-MBE). The AlN buffer layer containing both $c$-plane and $M$-plane AlN was grown by RF magnetron sputter on a sapphire substrate before growing GaN. The growth direction of GaN is [1\underline {1}00] oriented ($M$-plane) instead of [0001] oriented ($c$-plane). It was found that the $c$-plane GaN disappeared for higher growth temperature and the zinc-blende GaN appeared. The band gap was changed when we tuned III/V ratio. The crystal characteristics of GaN films for different growth parameters were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM),photoluminescence (PL), X-ray diffraction (XRD),and reflection high-energy electron diffraction (RHEED).