Enhanced ultraviolet photoconductivity in semiconducting ZnGa2O4 thin films

Abstract

We have investigated the conductivity and photoconductivity response of undoped and Li-doped ZnGa2O4 epitaxial films grown using pulsed-laser deposition. A significant enhancement of the ultraviolet (UV) photoresponse is observed with Li doping that also correlates with an enhanced luminescent intensity. The wavelength dependence observed for creation of free carriers under UV excitation suggests that the transition is either band-to-band or involves a defect level near the band edge. Moderate n-type dark conductivity is observed for undoped films processed under reducing conditions. With Li doping, dark conductivity is reduced, suggesting that lithium ions in the zinc gallate lattice serve as deep acceptors. In addition, Li doping effectively eliminates persistent photoconductivity that is commonly observed in undoped films, suggesting the possible use of Li-doped ZnGa2O4 as a visible wavelength blind UV photodetector.