Structures of nitridated layers on sapphire studied by x-ray reflectivity and diffraction

Abstract

A nitridated layer of c-plane sapphire was studied by using synchrotron x-ray reflectivity and diffraction measurements. The nitridation of the sapphire surface produced an epitaxial AlN layer with a low mosaicity (1 arcmin) normal to the surface. The nitridation temperature determined the limiting thickness for the nitridated layer. Excessive nitridation beyond the limiting thickness caused strain relaxation by a reduction of lateral domain size and an increase in lateral mosaicity. Therefore, the nitridated layer with compressive strain may provide better nucleation sites for the subsequent GaN overlayer growth than the strain-relaxed one.