The early stages of thermal oxidation of gallium nitride epilayers in dry O
-2 have been studied using surface sensitive analytical techniques and tran
smission electron microscopy. Deconvolution of the Ga 3d core level spectra
from X-ray photoelectron spectroscopy revealed peak positions representing
gallium nitride, gallium oxide, and an intermediate phase. Transmission el
ectron microscopy revealed an overlayer approximately 1.5-3.0 nm thick with
registry to the (0001) GaN after dry oxidation at 800 degrees C for 1 h. B
ased on the data from X-ray photoelectron spectroscopy, this layer is belie
ved to be a Ga(x+2)N3xO(3-3x) compound. Atomic force microscopy and transmi
ssion electron microscopy revealed the formation of discrete oxide crystall
ites on top of the oxynitride layer. The crystallites become more numerous
and grow with continued oxidation. (C) 2000 Published by Elsevier Science S
.A. All rights reserved.