Deep-center hopping conduction in GaN

Molecular-beam-epitaxial GaN layers change from strongly conductive (rho similar or equal to = 10(-2) Ohm cm at 300 K) to semi-insulating (rho similar or equal to 10(6) Ohm cm) as the N flux is increased. Layers grown at low fluxes show strong n-type conduction, with transport in the conduction band at high temperatures and in a shallow donor band at low temperatures. For layers grown at high N fluxes, the Hall coefficients become too small to measure, suggesting hopping conduction among deep centers. The temperature-dependent resistivity data are most consistent with multiphonon, rather than single-phonon, hopping. (C) 1996 American Institute of Physics.