The 2D InSe/WS2 Heterostructure with Enhanced Optoelectronic Performance in the Visible Region**Supported by the National Natural Science Foundation of China under Grant Nos 11404013, 11474012, 11364030, 61622406, 61571415, 51502283 and 11605003, the National Key Research and Development Program of China under Grant No 2017YFA0206303, the MOST of China, and the 2018 Graduate Research Program of Beijing Technology and Business University.

Abstract

Two-dimensional (2D) InSe and WS2 exhibit promising characteristics for optoelectronic applications. However, they both have poor absorption of visible light due to wide bandgaps: 2D InSe has high electron mobility but low hole mobility, while 2D WS2 is on the contrary. We propose a 2D heterostructure composed of their monolayers as a solution to both problems. Our first-principles calculations show that the heterostructure has a type-II band alignment as expected. Consequently, the bandgap of the heterostructure is reduced to 2.19 eV, which is much smaller than those of the monolayers. The reduction in bandgap leads to a considerable enhancement of the visible-light absorption, such as about fivefold (threefold) increase in comparison to monolayer InSe (WS2) at the wavelength of 490 nm. Meanwhile, the type-II band alignment also facilitates the spatial separation of photogenerated electron-hole pairs; i.e., electrons (holes) reside preferably in the InSe (WS2) layer. As a result, 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 WS2 monolayers, respectively.