PRECONDITIONING OF C-PLANE SAPPHIRE FOR GAN EPITAXY BY RADIO-FREQUENCY PLASMA NITRIDATION

The crystalline quality of molecular beam epitaxy grown layers of GaN on sapphire is generally improved by nitridation of the substrate. In this study, we use x-ray photoelectron spectroscopy, low energy electr on diffraction, and atomic force microscopy to examine the case for ni tridation of c-plane sapphire upon exposure to rf plasma generated nit rogen radicals. We find that a monolayer of surface nitride is formed after similar to 300 min exposure with the substrate at 400 degrees C. Extended exposure causes growth of protrusions from the c-plane sapph ire and thus leads to a rough surface morphology. Moreover, we report removal of adventitious surface carbon upon heat treatment at 300 degr ees C in nitrogen plasma, albeit with reduced efficiency compared with hydrogen plasma cleaning. (C) 1997 American Institute of Physics.