Transport and trap states in proton irradiated ultra-thick kappa-Ga2O3

Changes induced by irradiation with 1.1 MeV protons in the transport properties and deep trap spectra of thick (>80 mu m) undoped kappa-Ga2O3 layers grown on sapphire are reported. Prior to irradiation, the films had a donor concentration of similar to 10(15) cm(-3), with the two dominant donors having ionization energies of 0.25 and 0.15 eV, respectively. The main electron traps were located at E-c-0.7 eV. Deep acceptor spectra measured by capacitance-voltage profiling under illumination showed optical ionization thresholds near 2, 2.8, and 3.4 eV. The diffusion length of nonequilibrium charge carriers for epsilon-Ga2O3 was 70 +/- 5 nm prior to irradiation. After irradiation with 1.1 MeV protons to a fluence of 10(14) cm(-2), there was total depletion of mobile charge carriers in the top 4.5 mu m of the film, close to the estimated proton range. The carrier removal rate was 10-20 cm(-1), a factor of 5-10 lower than in beta-Ga2O3, while the concentration of deep acceptors in the lower half of the bandgap and the diffusion length showed no significant change.