GaN-based nanowire photodetectors

Abstract

In this work, we present a comprehensive study of the photocurrent phenomena in single defect-free GaN nanowires (NWs), analyzing the effect of the contact nature, excitation power, light polarization, measuring frequency, and environment. GaN NWs present high photocurrent gain, in the range of 1E5-1E8, with the photocurrent increasing sublinearly with the excitation power. The spectral response is relatively flat for excitation above the GaN bandgap and presents a visible rejection of more than six orders of magnitude. In depleted nanowires (diameter < 100 nm), the photocurrent time response is in the milisecond range, far from the persistent photoconductivity effects (seconds, minutes) observed in larger NWs or two-dimensional layers. From the above-described results, we confirm that the photoresponse is dominated by the redistribution of charge at the surface levels. However, the total depletion of the NW active region reduces the surface band bending preventing persistent photoconductivity effects and granting insensitivity to the chemical environment.