Formation of Near-IR Excitons in Low Dimensional CuSbS$_2$

TL;DR

This study investigates the optical properties of low-dimensional CuSbS$_2$, revealing that despite thickness reduction, the optical gap remains stable, and near-infrared excitons form due to quantum confinement and surface states.

Contribution

The paper provides a theoretical explanation for the stable optical gap and exciton formation in thin CuSbS$_2$ layers using advanced computational methods.

Findings

Optical gap remains at about 1.5 eV across different thicknesses.

Strongly bound near-infrared excitons form in thin layers.

Surface states and quantum confinement influence optical properties.

Abstract

The electronic and optical properties of low-dimensional semiconductors are typically quite different from those of their bulk counterparts. Yet, the optical gap of two-dimensional copper antimony disulfide (CuSbS$_2$) does not dramatically change with decreasing thickness of the material. The absorption onset remains at about 1.5 eV in the monolayer, bilayer, and bulk materials. Using density functional theory and many-body perturbation theory, we rationalize this behavior through the interplay of quantum confinement, electron-hole interactions, and the formation of surface states. Specifically, the spatial confinement in thin layers induces strongly bound optical transitions in the near-infrared region. Our results explain the optical properties in copper antimony disulfide platelets of varying thickness and set these materials as potential candidates for novel photovoltaic devices and near-infrared sensors.