The study of hydrogenation effect for the deep levels in GaN epilayers

After the undoped GaN epilayers were grown on (0 0 0 1) sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE), the photoconductivity (PC) and thermally stimulated current (TSC) measurements have been carried out so as to investigate the hydrogenation and annealing effect of the deep levels. These results indicate that the values of concentrations of the deep levels in the GaN epilayers decrease by the passivation of hydrogenation in both PC and TSC measurements. After hydrogenation, the PC intensity for the hydrogenated GaN epilayer decreased remarkably in comparison with that for the as-grown sample and the TSC peak near 150 K drastically decreased. case of PC measurement, the PC intensity for the hydrogenated and annealed GaN epilayer was approximately half that for the hydrogenated only GaN epilayer when the hydrogenated epilayer was annealed at 700°C. This result reveals that the passivation of the deep levels due to the hydrogenation is still effective at the annealing temperature of 700°C. In the case of TSC measurement, the deep levels changed slightly in comparison with that of hydrogenated GaN epilayer when the hydrogenated GaN epilayer was annealed at 600°C for 30 s. This result also shows that the passivation of deep levels due to the hydrogenation is still effective at the annealing temperature of 600°C for 30 s. In considering the above circumstances, these TSC results are in reasonable agreement with the PC results.