The impurity size-effect and phonon deformation potentials in wurtzite GaN

Doping induced changes in lattice parameters are investigated experimentally for the shallow donors silicon and germanium in thin-film wurtzite a-plane GaN. Silicon doping results in a lattice contraction while germanium doping results in a small but measurable lattice expansion. By high-resolution x-ray diffraction, we are able to determine the isotropically averaged size-effect with high accuracy. The analysis procedure yields en passant results for the phonon deformation potentials cE1(TO) and cE2h.