Au and Ag Schottky contacts on the epiready (0001)Zn surface of bulk n-ZnO crystals show Schottky barrier heights of 0.65–0.70 eV from capacitance–voltage measurements, activation energies for reverse saturation currents of 0.3–0.4 eV and saturation current densities ranging from 10−5 A cm−2 on surfaces etched in HCl to 8×10−7 A cm−2 on solvent cleaned samples. The diode ideality factors were in the range 1.6–1.8 under all conditions. The properties of both the Au and the Ag Schottky diodes were degraded by heating in vacuum to temperatures even as low as 365 K. The degradation mechanisms during annealing were different in each case, with the Au showing reaction with the ZnO surface and the Ag contacts showing localized delamination. Mechanical polishing of the ZnO surface prior to contact deposition produced a high-resistivity damaged layer with prominent deep level defects present with activation energies of 0.55 and 0.65 eV.

Deep electron and hole traps in 10 MeV proton irradiated high-quality b-Ga 2 O 3 films grown by Hydride Vapor Phase Epitaxy (HVPE) on bulk b-Ga 2 O 3 substrates were measured by deep level transient spectroscopy with electrical and optical injection, capacitance-voltage profiling in the dark and under monochromatic irradiation, and also electron beam induced current. Proton irradiation caused the diffusion length of charge carriers to decrease from 350-380 lm in unirradiated samples to 190 lm for a fluence of 10 14 cm À2 , and this was correlated with an increase in density of hole traps with optical ionization threshold energy near 2.3 eV. These defects most likely determine the recombination lifetime in HVPE b-Ga 2 O 3 epilayers. Electron traps at E c-0.75 eV and E c-1.2 eV present in as-grown samples increase in the concentration after irradiation and suggest that these centers involve native point defects.

Carrier removal rates and electron and hole trap densities in β-Ga2O3 films grown by hydride vapor phase epitaxy (HVPE) and irradiated with 18 MeV α-particles and 20 MeV protons were measured and compared to the results of modeling. The electron removal rates for proton and α-radiation were found to be close to the theoretical production rates of vacancies, whereas the concentrations of major electron and hole traps were much lower, suggesting that the main process responsible for carrier removal is the formation of neutral complexes between vacancies and shallow donors. There is a concurrent decrease in the diffusion length of nonequilibrium charge carriers after irradiation, which correlates with the increase in density of the main electron traps E2* at Ec − (0.75–0.78) eV, E3 at Ec − (0.95–1.05) eV, and E4 at Ec − 1.2 eV. The introduction rates of these traps are similar for the 18 MeV α-particles and 20 MeV protons and are much lower than the carrier removal rates.

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Hole traps in hydride vapor phase epitaxy β-Ga2O3 films were studied by deep level transient spectroscopy with electrical and optical excitation (DLTS and ODLTS) and by photocapacitance and temperature dependence measurements. Irradiation with 20 MeV protons creates deep electron and hole traps, a strong increase in photocapacitance, and prominent persistent photocapacitance that partly persists above room temperature. Three hole-trap-like signals H1 [self-trapped holes (STH)], H2 [electron capture barrier (ECB)], and H3, with activation energies 0.2 eV, 0.4 eV, 1.3 eV, respectively, were detected in ODLTS. The H1 (STH) feature is suggested to correspond to the transition of polaronic states of STH to mobile holes in the valence band. The broad H2 (ECB) feature is due to overcoming of the ECB of the centers responsible for persistent photocapacitance for temperatures below 250 K. The H3 peak is produced by detrapping of holes from Ev + 1.3 eV hole traps believed to be related to gallium vacancy acceptors. One more deep acceptor with optical ionization threshold near 2.3 eV is likely responsible for high temperature persistent photocapacitance surviving up to temperatures higher than 400 K. The latter traps show a significant barrier for capture of electrons.