Photocurrent generation in a metallic transition-metal dichalcogenide

Abstract

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-$\mathrm{Nb}{\mathrm{S}}_{2}$ thin crystals using scanning photocurrent microscopy (SPCM) both at zero and finite bias. SPCM measurements reveal that the photocurrent predominantly emerges from metal/$\mathrm{Nb}{\mathrm{S}}_{2}$ junctions of the two-terminal device at zero bias. At finite biases, along with the photocurrent generated at metal/$\mathrm{Nb}{\mathrm{S}}_{2}$ junctions, now a negative photoresponse from all over the $\mathrm{Nb}{\mathrm{S}}_{2}$ 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 $\mathrm{Nb}{\mathrm{S}}_{2}$ is among a few metallic materials in which photocurrent generation is possible.