Mechanisms of photoconductivity in atomically thin MoS2

TL;DR

This study investigates the mechanisms of photoconductivity in atomically thin MoS2 transistors, revealing photovoltaic and photoconductive effects, and provides a model to guide the design of MoS2-based photodetectors.

Contribution

It identifies and models the photovoltaic and photoconductive effects in MoS2 transistors, offering strategies for improved atomically thin photodetector design.

Findings

Both photovoltaic and photoconductive effects show strong photogain.

Photovoltaic effect involves charge transfer to molecules like water.

Photoconductive effect is due to carrier trapping in band tail states.

Abstract

Atomically thin transition metal dichalcogenides have emerged as promising candidates for sensitive photodetection. Here, we report a photoconductivity study of biased mono- and bilayer molybdenum disulfide field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photogain. The photovoltaic effect is described as a shift in transistor threshold voltage due to charge transfer from the channel to nearby molecules, including SiO2 surface-bound water. The photoconductive effect is attributed to the trapping of carriers in band tail states in the molybdenum disulfide itself. A simple model is presented that reproduces our experimental observations, such as the dependence on incident optical power and gate voltage. Our findings offer design and engineering strategies for atomically thin molybdenum disulfide photodetectors, and we anticipate that the results are generalizable to other transition metal dichalcogenides as well.