Quasiparticle band alignment and stacking-independent exciton in MA$_2$Z$_4$ (M = Mo, W, Ti; A= Si, Ge; Z = N, P, As)

TL;DR

This study uses advanced ab initio methods to analyze the electronic structure and excitonic properties of a family of two-dimensional materials, revealing significant differences from DFT predictions and consistent band alignment types.

Contribution

It provides a systematic GW and Bethe-Salpeter analysis of MA$_2$Z$_4$ monolayers, highlighting the importance of quasiparticle effects beyond DFT.

Findings

GW predicts larger band gaps than DFT.

Band alignments are consistent between GW and DFT.

Excitonic properties are characterized independently of stacking.

Abstract

Motivated by the recently synthesized two-dimensional semiconducting MoSi$_2$N$_4$, we systematically investigate the quasiparticle band alignment and exciton in monolayer MA$_2$Z$_4$ (M = Mo, W, Ti; A= Si, Ge; Z = N, P, As) using ab initio GW and Bethe-Salpeter equation calculations. Compared with the results from density functional theory (DFT), our GW calculations reveal substantially more significant band gaps and different absolute quasiparticle energy but predict the same types of band alignments.