Polarization dependent X-ray absorption studies of the chemical bonds anisotropy in wurtzite GaN grown at different conditions

Polarization-dependent X-ray absorption spectroscopy was used to examine th e influence of crystal growth techniques and substrates type on the bond le ngths and the bond structure of the single crystalline, wurtzite GaN in a f orm of bulk materials and epitaxial layers. The layers were grown by molecu lar beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) o n different substrates such as SiC, sapphire and GaN, From the observed X-r ay absorption near edge structure (XANES) of the Ga K-edges, it was found t hat MOCVD introduces a stronger disorder around Ga atoms than MBE. Comparin g the Ga and N K-edges of the epilayers and the bulk crystal, we found a pr evailing contribution of N-vacancies in the layers and dominance of Ga-vaca ncies in the bulk crystal. The bonds along the c-axis are less perfect than the bonds in the c-plane for all investigated epilayers. The per-formed st andard extended X-ray absorption fine structure analysis (EXAFS) resulted i n a direct estimate of the bond lengths in the c-plane and along the c-axis . (C) 2001 Elsevier Science BM All rights reserved.