Mechanisms of Photoconductivity in Atomically Thin\nMoS₂

Abstract

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