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

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. The O2 plasma acts to induce the p-type WSe2 for the otherwise n-type WSe2 by forming tungsten oxide (WOx) layer upon the O2 plasma-treatment. The WSe2 lateral pn-homojunctions displayed an enhanced photoresponse and resulted in open-circuit voltage (VOC) and short-circuit current (ISC) originated from the pn junction formed after O2 plasma-treatment. We further notice that the amplitude of photocurrent can be modulated by different gate bias. The fabricated WSe2 pn-homojunctions exhibit greater photoresponse with photoresponsivities (ratio of the photocurrent and the incident laser power) of 250 mA/W and 2000 mA/W, high EQE (%, total number of charge carriers generated for the number of incident photons on photodetectors) of 97 % and 420 %, and superior Detectivity (magnitude of detector sensitivity) of 7.7 x 109 Jones and 7.2 x 1010 Jones up on illumination with visible (520 nm) and near infrared (NIR) lasers (852 nm), respectively at low bias (Vg = 0 V and Vd = 1 V) at room temperature demonstrating very high-performance in the IR region superior to the contending 2D materials 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 photo-carriers with applied external drain bias upon the strong light absorption.