Effects of hydrogenation and annealing on the deep levels in GaN epilayers grown on sapphire substrates

The photoionization cross section and the concentration of state of the deep levels in as-grown, hydrogenated, and hydrogenated and annealed GaN epilayers were determined from the dependence of the rise and the decay times of the extrinsic photoconductivity (PC) response on the post treatment condition. The values of the concentrations of the deep levels in the GaN epilayer decreased by the hydrogenation and the annealing treatment. While the thermal activation energy of the deep level, which were determined from the temperature dependence of the relaxation rimes of the extrinsic PC response, for the hydrogenated GaN/sapphire heterostructure decreased in comparison with that for the as-grown sample, that for the hydrogenated and annealed sample increased in comparison with that for the hydrogenated sample.