DEEP-CENTER HOPPING CONDUCTION IN GAN

Molecular-beam-epitaxial GaN layers change from strongly conductive (r ho similar or equal to = 10(-2) Ohm cm at 300 K) to semi-insulating (r ho similar or equal to 10(6) Ohm cm) as the N flux is increased. Layer s 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 coeff icients become too small to measure, suggesting hopping conduction amo ng deep centers. The temperature-dependent resistivity data are most c onsistent with multiphonon, rather than single-phonon, hopping. (C) 19 96 American Institute of Physics.