Photocurrent generation in a metallic transition-metal dichalcogenide

Photocurrent generation is unexpected in metallic 2D layered materials unless a photothermal mechanism is prevalent. Yet, typical high thermal conductivity and low absorption of the visible spectrum prevent photothermal current generation in metals. Here, we report photoresponse from two-terminal devices of mechanically exfoliated metallic 3R-NbS2 thin crystals using scanning photocurrent microscopy (SPCM) both at zero and finite bias. SPCM measurements reveal that the photocurrent predominantly emerges from metal/NbS2 junctions of the two-terminal device at zero bias. At finite biases, along with the photocurrent generated at metal/NbS2 junctions, now a negative photoresponse from all over the NbS2 crystal is evident. Among our results, we realized that the observed photocurrent can be explained by the local heating caused by the laser excitation. These findings show that NbS2 is among a few metallic materials in which photocurrent generation is possible.