Anisotropic to Isotropic Transition in Monolayer Group-IV Tellurides.

Qian Wang,Alexander Urban,Pengfei Lu,Huawei Cao,Liyuan Wu

doi:10.3390/ma14164495

Abstract

Monolayer group-IV tellurides with phosphorene-derived structures are attracting increasing research interest because of their unique properties. Here, we systematically studied the quasiparticle electronic and optical properties of two-dimensional group-IV tellurides (SiTe, GeTe, SnTe, PbTe) using the GW and Bethe–Salpeter equation method. The calculations revealed that all group-IV tellurides are indirect bandgap semiconductors except for monolayer PbTe with a direct gap of 1.742 eV, while all of them are predicted to have prominent carrier transport ability. We further found that the excitonic effect has a significant impact on the optical properties for monolayer group-IV tellurides, and the predicted exciton binding energy is up to 0.598 eV for SiTe. Interestingly, the physical properties of monolayer group-IV tellurides were subject to an increasingly isotropic trend: from SiTe to PbTe, the differences of the calculated quasiparticle band gap, optical gap, and further exciton binding energy along different directions tended to decrease. We demonstrated that these anisotropic electronic and optical properties originate from the structural anisotropy, which in turn is the result of Coulomb repulsion between non-bonding electron pairs. Our theoretical results provide a deeper understanding of the anisotropic properties of group-IV telluride monolayers.

Highlights

Published: 11 August 2021Group IV–VI compounds, such as PbTe, GeTe, and SnTe, have been used as the functional materials in optoelectronic and thermoelectric devices for a long time because of their effective suitable bandgaps and high Seebeck coefficients [1,2,3]
PreFirst, we considered the structural properties of group-IV telluride monolayers
The differences in the calculated quasiparticle bandgap, Bethe–Salpeter equation (BSE) optical gap, and exciton binding energy in different directions tended to decrease from SiTe to SnTe, while the band structure and optical property exhibited totally isotropic behaviors for PbTe monolayer, which is the consequence of vanishing structural anisotropy

Summary

Introduction

Group IV–VI compounds, such as PbTe, GeTe, and SnTe, have been used as the functional materials in optoelectronic and thermoelectric devices for a long time because of their effective suitable bandgaps and high Seebeck coefficients [1,2,3]. Zhang et al predicted that the unequal lattice constants and relative atomic displacements are responsible for ferroelectricity in monolayer GeTe, SnTe, and the non-ferroelectric nature of monolayer PbTe [44]. These findings indicate that structural anisotropy has a profound influence on the physical properties of this system. We systematically study the quasiparticle band structures and optical properties of group-IV tellurides (SiTe, GeTe, SnTe, PbTe) by means of predictive calculations based on the accurate many-body perturbation GW theory and the Bethe–Salpeter equation. To obtain insights into the structural anisotropy, we explore the bond nature in the compounds by analyzing the electron localization functions and charge density

Computational Details

Geometry Structures

Quasiparticle

Optical Properties of Monolayer Group-IV Tellurides

Conclusions