Photosensitivity of Ga2O3 Schottky diodes: Effects of deep acceptor traps present before and after neutron irradiation

The photocurrent produced by 259 nm wavelength excitation was measured in beta-Ga2O3 Schottky diodes before and after neutron irradiation. These samples differed by the density of deep acceptors in the lower half of the bandgap as detected by capacitance-voltage profiling under monochromatic illumination. Irradiation led to a very strong increase in photocurrent, which closely correlated with the increase in deep trap density and the decrease after illumination of the effective Schottky barrier height due to hole capture by acceptors. A similar effect was observed on an as-grown beta s-Ga2O3 film with a high density of deep acceptors. Electron beam induced current measurements indicated a strong amplification of photocurrent, which is attributed to the Schottky barrier lowering by holes trapped on acceptors near the surface. Photocurrent build-up and decay curves show several time constants ranging from several milliseconds to many seconds. These characteristic times are attributed to tunneling of electrons into the hole-filled acceptors near the surface and to thermal emission of holes from deep acceptors.