Electronic properties and photo-gain of UV-C photodetectors based on high-resistivity orthorhombic κ-Ga2O3 epilayers

Abstract

Electrical and optical properties of nominally-undoped high-resistivity κ -Ga2O3 epitaxial films are presented, along with the ultraviolet detection performance of solar-blind photodetectors fabricated from these epilayers. The photodetectors exhibited a solar-blind rejection ratio higher than 104, reproducible on–off switching times and a remarkable photo-gain (up to 103). The latter can be ascribed to either a strong trapping effect of free holes by deep levels inducing a majority carrier excess Δn with respect to the minority carriers Δp, or to a hole mobility several orders of magnitude lower than the electron mobility, both the hypothesis being consistent with literature data. A saturation of the gain, dependent on detector size, was observed beyond a certain applied voltage, that is consistent with a minority carrier diffusion length of a few 10-5 cm.Non-critical growth conditions, reproducibility and intrinsic spectral selectivity together with good UV-detection performance make κ-Ga2O3 a suitable material for solar-blind ultraviolet photodetectors.