Ambient Effects on Photogating in MoS2 Photodetectors

TL;DR

This study investigates how ambient molecules like water and oxygen affect the photoresponse of MoS2 photodetectors, revealing that light-induced desorption of these molecules significantly influences device performance.

Contribution

It uncovers the mechanism by which adsorbates modulate photogating effects in MoS2, highlighting the role of molecular desorption under illumination.

Findings

Light illumination causes desorption of water and oxygen molecules from MoS2.

Molecular gating by adsorbed molecules dominates the photoresponse.

Desorption effects vary with wavelength and ambient conditions.

Abstract

Atomically thin transition metal dichalcogenides (TMDs) are ideal candidates for ultrathin optoelectronics that is flexible and semitransparent. Photodetectors based on TMDs show remarkable performance, with responsivity and detectivity higher than 10^3 A/W and 10^12 Jones, respectively, but they are plagued by response times as slow as several tens of seconds. Although it is well established that gas adsorbates such as water and oxygen create charge traps and significantly increase both the responsivity and the response time, the underlying mechanism is still unclear. Here we study the influence of adsorbates on MoS2 photodetectors under ambient conditions, vacuum and illumination at different wavelengths. We show that, for wavelengths sufficiently short to excite electron-hole pairs in the MoS2, light illumination causes desorption of water and oxygen molecules. The change in the molecular gating provided by the physisorbed molecules is the dominant contribution to the device photoresponse in ambient conditions.