Local structures of free-standing AlxGa1-xN thin films studied by extendedx-ray absorption fine structure

Local structural information for the first two atomic shells surrounding Ga atoms in free standing AlxGa1-xN alloy films has been obtained by extended x-ray absorption fine structure spectroscopy. For an AlN mole fraction ran ging from 0 to 0.6, we found that the first shell Ga-N bond length had only a weak composition dependence, roughly one quarter of that predicted by Ve gard's Law. In the second shell, the Ga-Ga bond length was significantly lo nger than that of Ga-Al (Delta similar to 0.04-0.065 Angstrom). A bond-type specific composition dependence was observed for the second shell cation-c ation distances. While the composition dependence of the Ga-Ga bond length is similar to 70% of that predicted by Vegard's Law, the Ga-Al bond length was essentially composition independent. These results suggested that local strain in AlxGa1-xN was also accommodated by lattice distortion in the Al cation sublattice. (C) 1999 American Institute of Physics. [S0003-6951(99)0 3852-8].