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.

The Fermi level in bulk semi-insulating β-Ga2O3 doped with Fe (∼5 × 1018 cm−3) is found to be pinned near Ec − 0.85 eV. At temperatures ≥400 K, Ni Schottky diodes showed good rectification and measurable low frequency capacitance, allowing the measurement of capacitance-frequency (C-f), capacitance-voltage (C-V), and capacitance-temperature (C-T) characteristics. The activation energy and the electron capture cross section obtained were (0.75–0.82) eV and (2–5) × 10−15 cm2, in good agreement with the reported signature of the E2 electron trap assigned to Fe. The concentration of the filled centers determined from C-V was close to the concentration of residual shallow donors in undoped materials. Photoinduced current transient spectroscopy measurements showed that Fe doping does not promote the generation of high densities of deep traps other than those related to Fe.

Epitaxial layers of α-Ga2O3 with different Sn doping levels were grown by halide vapor phase epitaxy on sapphire. The films had shallow donor concentrations ranging from 1017 to 4.8 × 1019 cm−3. Deep level transient spectroscopy of the lowest doped samples revealed dominant A traps with level Ec − 0.6 eV and B traps near Ec − 1.1 eV. With increasing shallow donor concentration, the density of the A traps increased, and new traps C (Ec − 0.85 eV) and D (Ec − 0.23 eV) emerged. Photocapacitance spectra showed the presence of deep traps with optical ionization energy of ∼2 and 2.7 eV and prominent persistent photocapacitance at low temperature, surviving heating to temperatures above room temperature. The diffusion length of nonequilibrium charge carriers was 0.15 µm, and microcathodoluminescence spectra showed peaks in the range 339–540 nm, but no band-edge emission.