Ultra-sensitive and selective VS2 phototransistor with the persistent photogenerated current tail

Recent development on VS2 related optical and electronic properties have proposed VS2 as the potential candidate for the two-dimensional transition metal dichalcogenides for optoelectronic applications. In the present work, CVD synthesized monolayer VS2 is used to demonstrate as the channel material for phototransistor fabrication with the 2 μm channel length. The extended Raman analysis shows that the monolayer VS2 consists of absorption coefficient of the order of 105 cm−1. The VS2 phototransistor is capable to senses the microwatt order of illumination and shows selectivity for the 540 nm (green) LED among the 450 (blue), 590 (orange), and 660 nm (red) LEDs. For the 540 nm LED, maximum responsivity reaches more than 46 A/W and detectivity more than 1.48 × 1011 jones for VGS and VDS = 2 V each. Responsibility and detectivity start to reduce with further enhancement of illumination from 5 μW/cm2, possibly due to the current saturation. The transient characteristics of the phototransistor under illumination show rise time of ∼4.2 s. While there is persistence of decaying drain current for longer time, the phototransistor demonstrates the trap state assisted photogating effect.