Light and bias-induced room temperature negative differential conductance in Ni-doped ZnO/p-Si Schottky photodiodes for quantum optical applications

We present evidence for the existence of bias and illumination-driven negative differential conductance (NDC) in Ni-doped aluminium/p-Silicon Schottky diodes. We suggest the Ridley–Watkins–Hilsum (RWH) mechanism as a possible explanation of the origin of this NDC. The NDC is dependent on the bias, doping level, and illumination. The dark currents do not show NDC regions, implying that it is a bias and illumination-dependent effect. We use surface plots to visually enhance the parametric trends in the output data. The resultant devices show excellent performance characteristics in both the photoconductive and the photovoltaic modes. The recently reported series resistance compensated method was applied to the I-V characteristics to extract the parameters of the diodes. The results show that Ni doping achieves NDC in reverse bias, between -1.5V to -0.5V, but only at certain doping levels in forward bias. The open circuit voltages of the devices in solar cell mode ranged from 0.03V to 0.6V.