Influencs of Surface V/III Ratio on the Film Quality during the GaN Growth in Gas-Source Molecular Beam Epitaxy

GaN growth was performed on 6H–SiC (0001) substrates by gas-source molecular beam epitaxy (GSMBE), using ammonia (NH3) and solid Ga as V and III sources. Two kinds of reflection high-energy electron diffraction (RHEED) patterns, namely (1×1) and (2×2), were observed during the GaN growth depending on the growth conditions, which correspond to nitrogen-rich and Ga-rich surfaces, respectively. Phase diagram of the two surface states via growth conditions was also obtained, indicating the surface V/III ratio change during the growth. It was found that the GaN film quality was greatly improved under nitrogen-rich growth conditions by X-ray diffraction (XRD) and photoluminescence (PL) characterizations.