Two-dimensional InSe/WS$_2$ heterostructure with enhanced optoelectronic performance in the visible region

TL;DR

This study designs a 2D InSe/WS2 heterostructure that exhibits enhanced visible-light absorption and improved charge separation, promising for optoelectronic applications, based on first-principles calculations.

Contribution

It introduces a novel 2D heterostructure with a direct band gap and improved optoelectronic properties, combining the advantages of InSe and WS2 monolayers.

Findings

The heterostructure has a direct band gap of 2.19 eV.

Visible-light absorption is increased fivefold at 490 nm.

Efficient spatial separation of electron-hole pairs is achieved.

Abstract

Two-dimensional (2D) InSe and WS$_2$ exhibit promising characteristics for optoelectronic and photoelectrochemical applications, e.g. photodetection and photocatalytic water splitting. However, both of them have poor absorption of visible light due to wide band gaps. 2D InSe has high electron mobility but low hole mobility, while 2D WS$_2$ is on the opposite. Here, we design a 2D heterostructure composed of their monolayers and study its optoelectronic properties by first-principles calculations. Our results show that the heterostructure has a direct band gap of 2.19 eV, which is much smaller than those of the monolayers mainly due to a type-II band alignment: the valence band maximum and the conduction band minimum of monolayer InSe are lower than those of monolayer WS$_2$, respectively. The visible-light absorption is enhanced considerably, e.g. about fivefold (threefold) increase at the wavelength of 490 nm in comparison to monolayer InSe (WS$_2$). The type-II band alignment also facilitates the spatial separation of photogenerated electron-hole pairs, i.e., electrons (holes) reside preferably in the InSe (WS$_2$) layer. The two layers complement each other in carrier mobilities of the heterostructure: the photogenerated electrons and holes inherit the large mobilities from the InSe and WS$_2$ monolayers, respectively.