Electronic and Optical Properties of Ta$_2$NiSe$_5$ Monolayer: A First-principles Study

TL;DR

This study uses first-principles calculations to explore the stability, electronic, and optical properties of Ta$_2$NiSe$_5$ monolayer, revealing its potential for infrared photodetection and polarization sensing due to stable excitonic features at room temperature.

Contribution

It provides the first detailed theoretical analysis of Ta$_2$NiSe$_5$ monolayer's properties, including stability, excitonic effects, and optical behavior, highlighting its application potential.

Findings

Monolayer is stable and can be exfoliated from bulk material.

Optically-active exciton with 66 meV binding energy exists at room temperature.

Inclusion of spin-orbit coupling is essential for accurate property prediction.

Abstract

The crystal structure, stability, electronic and optical properties of the Ta$_2$NiSe$_5$ monolayer have been investigated using first-principles calculations in combination with the Bethe-Salpeter equation. The results show that it is feasible to directly exfoliate a Ta$_2$NiSe$_5$ monolayer from the low-temperature monoclinic phase. The monolayer is stable and behaves as a normal narrow-gap semiconductor with neither spontaneous excitons nor non-trivial topology. Despite the quasi-particle and optical gaps of only 266 and 200 meV, respectively, its optically-active exciton has a binding energy up to 66 meV and can exist at room temperature. This makes it valuable for applications in infrared photodetection, especially its inherent in-plane anisotropy adds to its value in polarization sensing. It is also found that the inclusion of spin-orbit coupling is theoretically necessary to properly elucidate the optical and excitonic properties of monolayer.