Local Structure around Dopant Site in Ga-Doped ZnO from Extended X-ray Absorption Fine Structure Measurements

Abstract

The local structure around dopant sites in Ga-doped ZnO (GZO) films has been compared with that of Zn sites by means of X-ray absorption fine structure (XAFS) measurements. The near-edge part of XAFS (XANES) showed that the Ga 3+ ions occupied the Zn sites substitutionally in GZO. It was found, from the analysis of the extended part of XAFS (EXAFS), that the first nearest Ga–O distances were shorter than Zn–O distances, which is consistent with Ga 3+ having a smaller ionic radius than Zn 2+ . The next nearest Ga–Zn distances were found, on the contrary, to be longer than Zn–Zn distances. This agrees with the behavior of the lattice constants of GZO, which increase with Ga concentration. We argue that these behaviors are the result of a Coulomb interaction originating from the excess charge at the dopant Ga site, which does not arise in nonpolar solid solutions.