Enhancing photo-response performance through ultrathin Al2O3 modification at the p-SnO2:Al/n-GaN heterojunction interface

Abstract

We report on photoconductive and p-n heterojunction ultraviolet (UV) photodetectors based on p-type Al-doped SnO2 (p-SnO2:Al) thin films. We investigated the structural, optical, and electrical properties of Al-doped SnO2 thin films prepared using sol-gel methods, with our results being strongly supported by first-principles calculations. To achieve a self-powered photodetector device at zero bias, we fabricated p-SnO2:Al thin film on an n-GaN layer to form a p-n heterojunction. The responsivity of the p-n heterojunction UV detector, measured at zero bias, is 0.05 A/W, indicating good rectification properties. In order to improve device performance, a p-n heterojunction with a passivation layer was formed by inserting an ultrathin Al2O3 layer between the n-GaN layer and the p-SnO2:Al layer. With this change, the device's responsivity was 0.44 A/W at 350 nm at zero bias, roughly 10 times better than the detector without the Al2O3 passivation layer. The insertion of an ultrathin Al2O3 layer, which increases the efficiency of carrier separation on the SnO2 side while lowering the rate of carrier recombination at the interface, is responsible for the increased light responsivity performance.