Micro-Raman analysis of cubic GaN layers grown by MBE on (001) GaAs substrate

Cubic GaN layers are grown by molecular beam epitaxy on (001) GaAs substrat es. Optical micrographs of the GaN epilayers intentionally grown at Ga exce ss reveal the existence of surface irregularities such as bright rectangula r structures, dark dots surrounded by rectangles and dark dots without rect angles. Micro-Raman spectroscopy is used to study the structural properties of these inclusions and of the epilayers in greater detail. We conclude th at the observed irregularities are the result of a melting process due to t he existence of a liquid Ga phase on the growing surface.