Material properties of GaN grown by MOCVD

Abstract

n-Type GaN thin films grown by metal-organic chemical vapour deposition (MOCVD) were studied using photoluminescence (PL), photoreflectance (PR) and Raman scattering. In the PL spectra, the peak position of the band-edge transition shifts to the red side monotonically with increasing doping concentrations. It may be explained theoretically in terms of many-body effects, namely the renormalization of the bandgap. In the meantime, the line width of the PL peak is increased monotonically with the doping concentration. The luminescence line broadening can be modelled in terms of potential fluctuations caused by the random distribution of doping impurities. In the PR spectra the magnitude decreases monotonically with increasing doping concentration. This result can be explained by a simple model based on an assumption that low-density surface states exist in the surface of GaN. In the Raman scattering spectra, both A1(LO) mode and E2 mode were observed in the back scattering configuration. The A1(LO) mode shifted towards the high-frequency side and broadened with an increase in carrier concentration. This phenomenon can be interpreted by the LO phonon being coupled to the overdamped plasmon in GaN.