PRECONDITIONING OF C-PLANE SAPPHIRE FOR GAN MOLECULAR-BEAM EPITAXY BYELECTRON-CYCLOTRON-RESONANCE PLASMA NITRIDATION

Nitridation of c-plane sapphire is commonly employed in molecular beam epitaxy of GaN, in order to improve the crystalline quality of the de posited layers. In this study, we use x-ray photoelectron spectroscopy , Auger sputter profiling, reflection high energy electron diffraction , low energy electron diffraction, and atomic force microscopy to exam ine chemical and structural properties of sapphire (0001) substrate up on exposure to nitrogen activated by an electron cyclotron resonance p lasma source. Incorporation of nitrogen into the sapphire surface was verified with x-ray photoelectron spectroscopy, and a monolayer of sur face nitride is formed after approximately 60 min of nitridation at a substrate temperature of 620 degrees C. The thickness of the surface n itride layer is on the order of 4.5-6 Angstrom for nitridation times r anging from 60 to 180 min, as estimated from the recorded nitrogen Aug er sputter profiles. Reflection high energy electron diffraction gave clear evidence for formation of surface aluminum nitride, after prolon ged (60 min) nitridation. (C) 1998 American Institute of Physics. [S00 21-8979(98)07711-1].