Optical and structural properties of GaN films grown on c-plane Al2O3 by electron cyclotron resonance molecular beam epitaxy

Abstract

Optical and structural properties of undoped GaN films grown on Al2O3 (0 0 0 1) substrates under various nitrogen pressure and plasma power by electron cyclotron resonance molecular beam epitaxy were investigated by photoluminescence (PL) spectroscopy and X-ray diffraction (XRD). It was found that the optimum nitrogen pressure determined by full width at half maximum of XRD peak was in just agreement with that by PL spectra, and the GaN film grown under the optimum nitrogen pressure contains high density of dislocations. These results suggest that the optical quality is sensitive to the stress in the film and that the relaxation of stress depends on V/III ratio. We also found that the effects of increasing nitrogen pressure are not equivalent to the effects of increasing plasma power though they have been regarded as having the same effects.