# $h$-AlN-Mg(OH)$_{2}$ vdW Bilayer Heterostructure: Tuning the excitonic characteristics

## TL;DR

This study explores the structural, electronic, and optical properties of a $h$-AlN-Mg(OH)$_{2}$ van der Waals heterostructure, revealing tunable excitonic features and potential for light harvesting applications.

## Contribution

It provides a comprehensive theoretical analysis of the heterostructure's properties, highlighting the direct band gap, Type-II alignment, and excitonic behavior not previously detailed.

## Key findings

- Heterostructure prefers AB' stacking with direct band gap at Gamma.
- Presence of excitonic peaks only in the hetero-bilayer.
- First exciton peak is a spatially indirect exciton with electron and hole localized in different layers.

## Abstract

Motivated by recent studies that reported the successful synthesis of monolayer Mg(OH)$_{2}$ [Suslu \textit{et al.}, Sci. Rep. \textbf{6}, 20525 (2016)] and hexagonal (\textit{h}-)AlN [Tsipas \textit{et al}., Appl. Phys. Lett. \textbf{103}, 251605 (2013)], we investigate structural, electronic, and optical properties of vertically stacked $h$-AlN and Mg(OH)$_{2}$, through \textit{ab initio} density-functional theory (DFT), many-body quasi-particle calculations within the GW approximation, and the Bethe-Salpeter equation (BSE). It is obtained that the bilayer heterostructure prefers the $AB^{\prime}$ stacking having direct band gap at the $\Gamma$ with Type-II band alignment in which the valance band maximum and conduction band minimum originate from different layer. Regarding the optical properties, the imaginary part of the dielectric function of the individual layers and hetero-bilayer are investigated. The hetero-bilayer possesses excitonic peaks which appear only after the construction of the hetero-bilayer. The lowest three exciton peaks are detailedly analyzed by means of band decomposed charge density and the oscillator strength. Furthermore, the wave function calculation shows that the first peak of the hetero-bilayer originates from spatially indirect exciton where the electron and hole localized at $h$-AlN and Mg(OH)$_{2}$, respectively, which is important for the light harvesting applications.