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Changes induced by irradiation with 1.1 MeV protons in the transport properties and deep trap spectra of thick (>80 μm) undoped κ-Ga2O3 layers grown on sapphire are reported. Prior to irradiation, the films had a donor concentration of ∼1015 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 Ec−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 ɛ-Ga2O3 was 70 ± 5 nm prior to irradiation. After irradiation with 1.1 MeV protons to a fluence of 1014 cm−2, there was total depletion of mobile charge carriers in the top 4.5 μm 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 β-Ga2O3, while the concentration of deep acceptors in the lower half of the bandgap and the diffusion length showed no significant change. 

Abstract Films of α-Ga2O3 (Sn) grown by Halide Vapor Phase Epitaxy (HVPE) on sapphire with starting net donor densities in the range 5×1015- 8.4×1019 cm-3 were irradiated at room temperature with 1.1 MeV protons to fluences from 1013 -1016 cm-2. For the lowest doped samples, the carrier removal rate was ~35 cm-1 at 1014 cm-2 and ~1.3 cm-1 for 1015 cm-2 proton fluence. The observed removal rate could be accounted for by the introduction of deep acceptors with optical ionization energies of 2 eV, 2.8 eV and 3.1 eV. For doped samples doped at 4x1018 cm-3, the initial electron removal rate was 5×103 cm-1 for 1015 cm-2 proton fluence and ~300 cm-1 for 1016 cm-2 proton fluence. The same deep acceptors were observed in photocapacitance spectra, but their introduction rate was orders of magnitude lower than the carrier removal rate. For the heaviest doped samples, an electron removal rate could be measured only after irradiation with the highest proton fluence of 1016 cm-2 and was close to that measured for the 4×1018 cm-3 sample after exposure to the same fluence. Possible reasons for the observed behavior are discussed and radiation tolerances of lightly doped α-Ga2O3 films is higher than for similarly doped β-Ga2O3 layers.