Composition-dependent absorption of radiation in semiconducting MSi2Z4 Monolayers

TL;DR

This study uses advanced first-principles calculations to explore the electronic and optical properties of MSi2Z4 monolayers, revealing their potential for optoelectronic applications due to their tunable band gaps and high photoluminescence efficiency.

Contribution

It provides a comprehensive theoretical analysis of the electronic structure and optical absorption of MSi2Z4 monolayers, highlighting their unique features and application potential.

Findings

All monolayers have a direct band gap except MoSi2N4.

Tungsten-based compounds show broader band gap tunability.

Materials exhibit strong excitonic effects and potential for high photoluminescence.

Abstract

The recent synthesis of MoSi2N4 material, along with theoretical predictions encompassing the entire family of chemical analogs, has opened up a new array of low-dimensional materials for a diverse range of optoelectronics and photovoltaics applications. In this study, we conducted state-of-the-art many-body first-principles calculations to analyze the quasi-particle electronic structure of the material class MSi2Z4 (where M = Mo, W, and Z = N, P, As, Sb). All monolayers display a direct band gap at the K point, with the exception of MoSi2N4. In tungsten-based compounds, the fundamental-gap can be adjusted over a significantly broader energy range compared to their molybdenum-based counterparts. Additionally, increasing atomic weight of the Z, both the band gap and exciton binding energies decrease. A noteworthy feature is the absence of a lateral valley ({\Lambda} or Q) near the conduction band minimum, indicating potential higher photoluminescence efficiencies compared to conventional transition-metal dichalcogenide monolayers. The optical spectra of these materials are predominantly characterized by tightly bound excitons, leading to an absorption onset in the visible range (for N-based) and in the infrared region (for others). This diversity offers promising opportunities to incorporate these materials and their heterostructures into optoelectronic devices, with tandem solar cells being particularly promising.