Unpinning the Fermi level of GaN nanowires by ultraviolet radiation

Abstract

We observe a significant increase in the photoluminescence intensity of GaN nanowires under continuous ultraviolet irradiation on a time scale of minutes. Experiments carried out under different ambient conditions demonstrate that this increase is caused by the photoinduced desorption of oxygen from the nanowire sidewalls. The slow, highly nonexponential temporal evolution of the photoluminescence signal is modeled by a random-walk approach. The model reveals that already desorbed oxygen molecules are likely to be readsorbed at adjacent nanowires. Time-resolved photoluminescence measurements are performed to unravel the correlation between the oxygen desorption and the increase in the photoluminescence intensity. We find that the oxygen desorption unpins the Fermi level, which in turn leads to an increase in quantum efficiency by enhancing the radiative decay of excitons.