Study of lattice deformation and atomic bond length for AlxGa1−xN epi-layers with synchrotron radiation X-ray absorption spectroscopy

Abstract

The lattice deformation in wurtzite AlxGa1−xN epi-layers (0.19 ≤ x ≤ 0.58) grown on sapphire substrates by metal organic chemical vapor deposition has been studied with synchrotron radiation X-ray absorption spectroscopy and X-ray diffraction. The result reveals that Al substitution for Ga in AlGaN epi-layers induces a significant contraction in crystal lattice and c/a ratio (c and a are the lattice constants for AlGaN epi-layer, respectively), while the substitution only results in a slight expansion in internal parameter u, which is used to describe the lattice deformation of wurtzite structure. This fact suggests that u is not sensitive to Al substitution for Ga. A detailed analysis of extended X-ray absorption fine structure of Ga K-edge spectra show that the Ga–N bond length has only a weak composition dependence, while the Ga–Ga (Al) bond lengths are strongly dependent on the Al composition.