Detection of a high photoresponse at zero bias from a highly conducting ZnO:Ga based UV photodetector

Ga-doped ZnO (GZO) based ultraviolet photodetectors (PDs) were fabricated by dual ion beam sputtering with a metal-semiconductor-metal structure. The room-temperature operable PD demonstrated responsivity of 58 mA W^-1 at zero bias, which is 15 times larger than that reported on similar material grown by a different physical vapour deposition process, with internal and external quantum efficiency values of ∼22.5% and 37.4%. The unbiased photodetection is attributed to the tunnelling of electrons due to heavy doping of GZO and built-in electric field due to different barriers at the two metal semiconductor contacts. The asymmetry in the electrodes was investigated by temperature-dependent current-voltage measurements.