Optical properties of monolayer, multilayer, and bulk BiI$_3$ studied using time-dependent density functional theory

TL;DR

This study uses time-dependent density functional theory to analyze the optical properties of BiI$_3$ in monolayer, multilayer, and bulk forms, highlighting exciton presence only in the monolayer and confirming bulk properties with experimental data.

Contribution

It provides a detailed theoretical analysis of the layer-dependent optical properties of BiI$_3$, revealing exciton behavior exclusive to the monolayer and validating bulk optical characteristics.

Findings

Exciton observed only in monolayer BiI$_3$

Bulk BiI$_3$ has a visible light band gap consistent with experiments

Optical properties are layer-dependent, distinguishable via absorption spectra

Abstract

We investigate the optical property of monolayer and layered BiI$_3$ and reveal the presence of exciton only in the monolayer crystal. We evaluate the energy spectrum of a dielectric function by using time-dependent density functional theory. Bulk crystal of BiI$_3$ is an atomic layered semiconductor with the band gap corresponding to the frequency of visible light. The numerical result for the bulk crystal is confirmed to be consistent with the previous experimental results and it does not depend on the number of layers except the monolayer. We reveal the excitons appearing below the resonant peak associated with the inter-band excitation in the monolayer crystal. The unique optical property can be directly observed in the optical absorption or differential reflectance spectrum and distinguish the monolayer crystal from the stacked BiI$_3$.