Optical Properties of GaS-Ca(OH)$_2$ bilayer heterostructure

TL;DR

This study uses first-principle calculations to analyze the electronic and optical properties of GaS-Ca(OH)$_2$ heterostructures, revealing their potential for optoelectronic applications due to type-II band alignment and exciton behavior.

Contribution

It provides a detailed theoretical analysis of GaS-Ca(OH)$_2$ heterostructures, including band structure, optical properties, and stacking-dependent spectra, advancing understanding of their optoelectronic potential.

Findings

GaS-Ca(OH)$_2$ heterostructure has a significantly reduced band gap.

The heterostructure forms a type-II heterojunction facilitating charge separation.

Optical spectra vary with stacking type, enabling stacking identification.

Abstract

Finding novel atomically-thin heterostructures and understanding their characteristic properties are critical for developing better nanoscale optoelectronic devices. In this study, we investigate the electronic and optical properties of GaS-Ca(OH)$_2$ heterostructure using first-principle calculations. The band gap of the GaS-Ca(OH)$_2$ heterostructure is significantly reduced when compared with those of the isolated constituent layers. Our calculations show that the GaS-Ca(OH)$_2$ heterostructure is a type-II heterojunction which can be used to separate photoinduced charge carriers where electrons are localized in GaS and holes in the Ca(OH)$_2$ layer. This leads to spatially indirect excitons which are important for solar energy and optoelectronic applications due to their long lifetime. By solving the Bethe-Salpeter equation on top of single shot GW calculation (G$_0$W$_0$) the dielectric function and optical oscillator strength of the constituent monolayers and the heterostructure are obtained. The oscillator strength of the optical transition for GaS monolayer is an order of magnitude larger than Ca(OH)$_2$ monolayer. We also found that the calculated optical spectra of different stacking types of the heterostructure show dissimilarities, although their electronic structures are rather similar. This prediction can be used to determine the stacking type of ultra-thin heterostructures.