SURFACE-COMPOSITION AND STRUCTURE OF GAN EPILAYERS ON SAPPHIRE

The surface composition and structure of GaN films grown on sapphire s ubstrates by organometallic vapor-phase epitaxy (OMVPE) have been dete rmined through the use of time-of-flight scattering and recoiling spec trometry (TOF-SARS), classical ion trajectory simulations, and low-ene rgy electron diffraction (LEED). TOF-SARS spectra of scattered and rec oiled ions plus fast neutrals were collected using 4 keV Ar+ primary i ons. The scattering results were simulated by means of the three-dimen sional scattering and recoiling imaging code (SARIC). This data leads to the conclusions that both N-terminated {00 (1) over bar}-(1x1) and Ga-terminated {0001}-(1x1) surfaces occur, however no evidence was obt ained for mixed terminations. No relaxation or reconstruction was dete cted on either surface, although both surfaces exhibited two structura l domains. The {000 (1) over bar} surfaces are well-ordered and contai ned hydrogen atoms bound to the N atoms of the outermost layer. The (0 001) surfaces are highly reactive towards adsorption of carbon and oxy gen from residual gases, however unlike the {000 (1) over bar} surface s, they adsorb very little hydrogen. These Ga-terminated surfaces are stabilized and obtain more ordered structures as a result of the conta mination. (C) 1997 American Institute of Physics.