High Responsivity Gate Tunable UV-Visible Broadband Phototransistor Based on Graphene-WS2 Mixed Dimensional (2D-0D) Heterostructure

Abstract

Recent progress in the synthesis of highly stable, eco-friendly, cost-effective transition metal-dichalcogenides (TMDC) quantum dots (QDs) with their broadband absorption spectrum and wavelength selectivity features have led to their increasing use in broadband photodetectors. With the solution based processing, we demonstrate a super large (~ 0.75 mm^2), UV-Vis broadband (365-633 nm), phototransistor made of WS_2 QDs decorated CVD graphene as active channel with extraordinary stability and durability in ambient condition (without any degradation of photocurrent till 4 months after fabrication). Here, colloidal 0D WS_2-QDs are used as the photo absorbing material and graphene acts as the conducting channel. A high photoresponsivity (3.1 x 10^2 A/W), higher detectivity (2.2 x 10^12 Jones) and low noise equivalent power (4 x 10^{-14} W/Hz^0.5) are obtained at a low bias voltage (V_{ds} = 1V) at an illumination of 365 nm with an optical power as low as 0.8 \mu W/cm^2, which can further be tuned by modulating the gate bias. While comparing the photocurrent between two different morphologies of WS_2 (QDs and 2D nanosheets), a significant enhancement of photocurrent is observed in case of QDs based device. Ab initio density functional theory based calculations further support our observation, revealing the role of quantum confinement for the enhanced photo response. Our work reveals a strategy towards making a scalable, cost-effective, highly performing hybrid two-dimensional (2D/0D) photo detector with graphene-WS_2 QDs, paving the way towards the next generation optoelectronic applications.