Hole traps and persistent photocapacitance in proton irradiated β-Ga₂O₃ films doped with Si

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.