Abstract
GaN epilayers were grown on Al2O3(0001) substrate by electron cyclotron resonance molecular beam epitaxy. The effects of growth parameters such as growth temperature, nitrogen pressure, Ga cell temperature and substrate-surface nitridation on crystal quality were investigated by scanning electron microscope and X-ray diffraction. It was found that the formation of Ga droplets at the growth surface depends strongy on growth temperature and Ga cell temperature, and flat and smooth surfaces were obtained at the growth temperature of 750° C with the growth rate of 0.5 µ m/h. The III/V ratio has a large effect on the full width at half maximum (FWHM) of the X-ray diffraction (XRD), i.e., on the relaxation of misfit stress. However, substrate-surface nitridation has little effect on the relaxation of misfit stress.