Epilayers which had been nitrided for various times were investigated by using light-scattering tomography and Raman scattering. In light-scattering tomographic images of plan-view epilayers, the light-scattering defects were found to be distributed mainly in <11•0> directions. The density of the defects was lower in epilayers which had been nitrided for longer times. The defects were considered to be straight threading edge dislocations on {1¯1•0} planes. The Raman shift of the E2 mode was larger in samples which had been nitrided for longer times. The results demonstrated that misfit between the GaN epilayer and an Al2O3 substrate was more unfavourably accommodated by threading edge dislocations in epilayers which had been nitrided for longer times.

J.Kang, T.Ogawa: Applied Physics Letters, 1997, 71[16], 2304-6