Mg(OH)2 -WS2 Heterobilayer: Electric Field Tunable Bandgap Crossover

TL;DR

This study explores the electronic and optical properties of Mg(OH)2-WS2 heterobilayers, revealing electric field-induced bandgap crossover and potential for optoelectronic applications.

Contribution

It is the first to analyze the electric field tunability of the bandgap and excitonic properties in Mg(OH)2-WS2 heterobilayers using first principles calculations.

Findings

Both monolayers are direct-gap semiconductors.

Electric field induces a transition from staggered to straddling heterojunction.

Intralayer excitons have significantly larger oscillator strength than interlayer excitons.

Abstract

Magnesium hydroxide (Mg(OH)2) has a layered brucite-like structure in its bulk form and was recently isolated as a new member of 2D monolayer materials. We investigated the electronic and optical properties of monolayer crystals of Mg(OH)2 and WS2 and their possible heterobilayer structure by means of first principles calculations. It was found that both monolayers of Mg(OH)2 and WS 2 are direct-gap semiconductors and these two monolayers form a typical van der Waals heterostructure with a weak interlayer interaction and a type-II band alignment with a staggered gap that spatially seperates electrons and holes. We also showed that an out-of-plane electric field induces a transition from a staggered to a straddling type heterojunction. Moreover, by solving the Bethe-Salpeter equation on top of single shot G0 W0 calculations, we show that the oscillator strength of the intralayer excitons of the heterostructure is an order of magnitude larger than the oscillator strength of the interlayer excitons. Because of the staggered interfacial gap and the field- tunable energy band structure, the Mg(OH)2 -WS2 heterobilayer can become an important candidate for various optoelectronic device applications in nanoscale.