Optical study of cubic gallium nitride band-edge and relation with residual strain

A photoreflectance study of excitonic transitions in cubic GaN grown on cub ic SIC pseudo-substrates is reported. The determination of the temperature dependence of the two exciton energies is allowed by the rather low transit ion widths. Comparison of the two PR transition energies and widths with th eoretical calculation as a function of biaxial strain indicates that the lo west PR excitonic transition is composed of both contributions of light hol e and heavy hole valence band related excitons. The width of this transitio n is increasing as the residual strain in the layer increases the splitting between light and heavy hole valence bands.