Enhanced photodetector performance of SnO2/NiO heterojunction via Au incorporation

Abstract

Heterojunctions are known to have trap states and defects that are detrimental to the light responses, especially slowing down the rise and decay time. To address these issues in the charge transfer process, SnO2/NiO heterojunction was modified by incorporating Au at the surface and interface of different devices. The rectifying SnO2/NiO diode showed self-powered photodetector (SPD) characteristics when illuminated by 365 nm light and the responsivity obtained was 3 µA W−1. The 5 nm Au surface decorated SnO2/NiO diode showed the highest rectification ratio, 42.8 and the 2 nm Au decorated device showed 10.6 µA photocurrent generation. The 2 and 5 nm thick Au surface decoration resulted in the formation of nano-Schottky junctions with NiO. The embedding of Au at the interface of the SnO2/NiO diode showed a decrease in diode rectification. Two methods are used for Au incorporation at the interface; glancing angle deposition and electron beam evaporation followed by annealing. Unlike the glancing angle deposited Au film, the larger Au nanoparticles(NPs) formed by electron beam evaporation and annealing, and when embedded at SnO2/NiO interface, generated 9.6 µA of photocurrent and dark currents were lowered by one order. The modified diode characteristics were studied using impedance spectroscopy. The junction capacitance and time constant of Au incorporated devices were found to be much lower than that of bare SnO2/NiO heterojunction, leading to an improved response time and SPD performance. The responsivity, rise time, detectivity, and ON/Off ratio calculated for the device SnO2/NiO with Au NPs at the interface were 3.1 mA W−1, 1.6 s, 1.8 × 1010 Jones, and 2.6 × 103 respectively, best among all the devices. The heterojunction PDs with Au incorporation are a potential way to address the surface and interface effects at the nanoscale, thereby improving the device performance.