Gate-Modulated Ultrasensitive Visible and Near-Infrared Photodetection of Oxygen Plasma-Treated WSe₂ Lateral pn-Homojunctions

Abstract

We investigate the development of gate-modulated tungsten diselenide (WSe₂)-based lateral pn-homojunctions for visible and near-infrared photodetector applications via an effective oxygen (O₂) plasma treatment. O₂ plasma acts to induce the p-type WSe₂ for the otherwise n-type WSe₂ by forming a tungsten oxide (WO<i>_x</i>) layer upon O₂ plasma treatment. The WSe₂ lateral pn-homojunctions displayed an enhanced photoresponse and resulted in open-circuit voltage (<i>V</i>_OC) and short-circuit current (<i>I</i>_SC) originating from the pn-junction formed after O₂ plasma treatment. We further notice that the amplitude of the photocurrent can be modulated by different gate biases. The fabricated WSe₂ pn-homojunctions exhibit greater photoresponse with photoresponsivities (ratio of the photocurrent and incident laser power) of 250 and 2000 mA/W, high external quantum efficiency values (%, total number of charge carriers generated for the number of incident photons on photodetectors) of 97 and 420%, and superior detectivity values (magnitude of detector sensitivity) of 7.7 × 10⁹ and 7.2 × 10¹⁰ Jones upon illumination with visible (520 nm) and near-infrared lasers (852 nm), respectively, at low bias (<i>V</i>_g = 0 V and <i>V</i>_d = 1 V) at room temperature, demonstrating very high-performance in the IR region superior to the contending two-dimensional material-based photonic devices. These superior optoelectronic properties are attributed to the junctions induced by O₂ plasma doping, which facilitate the effective carrier generation and separation of photocarriers with applied external drain bias upon strong light absorption.