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

Recent progress in the synthesis of highly stable, eco-friendly, cost-effective transition-metal dichalcogenide (TMDC) quantum dots (QDs) with their broadband absorption spectra and wavelength selectivity features have led to their increasing use in broadband photodetectors. With the solution-based processing, we demonstrate a superlarge (∼0.75 mm2), ultraviolet–visible (UV–vis) broadband (365–633 nm) phototransistor made of WS2 QDs-decorated chemical vapor deposited (CVD) graphene as the active channel with extraordinary stability and durability under ambient conditions (without any degradation of photocurrent until 4 months after fabrication). Here, colloidal zero-dimensional (0D) WS2 QDs are used as the photoabsorbing material, and graphene acts as the conducting channel. A high photoresponsivity (3.1 × 102 A/W), moderately high detectivity (∼8.9 × 108 Jones), and low noise equivalent power (∼9.7 × 10–11 W/Hz0.5) are obtained at a low bias voltage (Vds = 1 V) at an illumination of 365 nm with optical power as low as ∼0.8 μW/cm2, which can be further tuned by modulating the gate bias. While comparing the photocurrent between two different morphologies of WS2 [QDs and two-dimensional (2D) nanosheets], a significant enhancement of photocurrent is observed in the case of QD-based devices. Ab initio density functional theory (DFT)-based calculations further support our observation, revealing the role of quantum confinement in enhanced photoresponse. Our work reveals a strategy toward developing a scalable, cost-effective, high-performance hybrid mixed-dimensional (2D-0D) photodetector with graphene-WS2 QDs for next-generation optoelectronic applications.