On the nature of photosensitivity gain in Ga2O3 Schottky diode detectors: Effects of hole trapping by deep acceptors

Highlights: • Deep acceptor states introduced into n-Ga₂O₃ by irradiation. This enables us to control, the density of these states. • Measurement of current collection efficiency show the capture of holes by deep acceptors gives rise to a decrease in Schottky barrier height and an increase of the electron current flow responsible for the observed high gain. • This mechanisms explains the high photoconductive gains reported in the literature for Ga₂O₃ photodetectors. • The reported observation could form a basis for improvement of photosensitivity of Ga₂O₃-based solar-blind photodetectors. -- Abstract: Lightly n-type doped Ga₂O₃ layers grown by Halide Vapor Phase Epitaxy (HVPE) on bulk n⁺-Ga₂O₃ substrates were subjected to irradiation with fast reactor neutrons, 20 MeV protons, or treatment in high ion density Ar plasma. These treatments lead to a marked increase in the concentration of deep acceptors in the lower half of the bandgap. These acceptors have optical ionization thresholds near 2.3 eV and 3.1 eV. There is a simultaneous strong enhancement of the photocurrent of Schottky diodes fabricated on these layers in the UV spectral range, and a large increase in the Electron Beam Induced Current (EBIC) collection efficiency. The gain in photocurrent at −10 V reached 18 times for neutron and proton irradiated samples, and 10⁴ times for the plasma treated samples. Similar increases in gain were observed in the EBIC current collection efficiency for beam energy 4 keV. With such beam energy, the electron–hole pairs are generated well within the space charge region. The results are explained by assuming that the capture of photoinduced or electron-beam-induced holes by the deep acceptors gives rise to a decrease in the effective Schottky barrier height and an increase of the electron current flow that is responsible for the observed high gain. The reported observation could form a basis for radical improvement of photosensitivity of Ga₂O₃-based solar-blind photodetectors. However, the photocurrent build-up and decay times in this mechanism are inherently long, on the order of some seconds.