Gallium K-edge EXAFS measurements on cubic and hexagonal GaN

The microstructure of undoped cubic and hexagonal GaN films is studied usin g temperature dependent Ga K-edge EXAFS measurements (10K-290K). The micros tructure around the Ga atom is distorted due to a splitting of the second n earest neighbor shell, which consists of Ga atoms. This splitting results i n an additional Ga path at a distance longer than expected by 0.8+/-0.05 A and is attributed to local lattice relaxation around nitrogen vacancies. Fr om the temperature dependence of the DW factors for the 2(nd) nearest neigh bor shell of Ga, the Einstein temperature is equal to 318+/-25K.