Coexistence of negative and positive photoconductivity in few-layer PtSe2 field-effect transistors

TL;DR

This study demonstrates that ultrathin PtSe_2 transistors exhibit both positive and negative photoconductivity, with environmental pressure controlling the dominant effect, and reveals the role of oxygen molecules in this process.

Contribution

It uncovers the coexistence of positive and negative photoconductivity in PtSe_2 transistors and explains the environmental control mechanism via oxygen molecule desorption.

Findings

Positive photoconductivity in vacuum converts to negative at higher pressure.

Oxygen molecules act as acceptors on the PtSe_2 surface.

Light irradiation causes oxygen desorption, reducing carrier density.

Abstract

Platinum diselenide (PtSe_2) field-effect transistors with ultrathin channel regions exhibit p-type electrical conductivity that is sensitive to temperature and environmental pressure. Exposure to a supercontinuum white light source reveals that positive and negative photoconductivity coexists in the same device. The dominance of one type of photoconductivity over the other is controlled by environmental pressure. Indeed, positive photoconductivity observed in high vacuum converts to negative photoconductivity when the pressure is rised. Density functional theory calculations confirm that physisorbed oxygen molecules on the PtSe_2 surface act as acceptors. The desorption of oxygen molecules from the surface, caused by light irradiation, leads to decreased carrier concentration in the channel conductivity. The understanding of the charge transfer occurring between the physisorbed oxygen molecules and the PtSe_2 film provides an effective route for modulating the density of carriers and the optical properties of the material.