Influences 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.