Observation of extremely long exciton lifetime in Janus-MoSTe monolayer

TL;DR

This study predicts that janus-MoSTe monolayer exhibits an exceptionally long exciton lifetime of about 1.31 nanoseconds, due to its built-in electric field and Coulomb screening, promising for optoelectronic applications.

Contribution

The paper introduces janus-MoSTe as a novel 2D TMD with a long exciton lifetime, analyzed through timedomain density functional theory, highlighting the role of electric fields in recombination dynamics.

Findings

Exciton lifetime of 1.31 ns in janus-MoSTe monolayer

Strong built-in electric field influences electron-hole dynamics

Potential for improved light detection and harvesting devices

Abstract

The electron-hole separation efficiency is a key factor that determines the performance of two-dimensional (2D) transition metal dichalcogenides (TMDs) and devices. Therefore, searching for novel 2D TMD materials with long timescale of carrier lifetime becomes one of the most important topics. Here, based on the timedomain density functional theory (TD-DFT), we propose a brand new TMD material, namely janus-MoSTe, which exhibits a strong build-in electric field. Our results show that in janus-MoSTe monolayer, the exciton consisting of electron and hole has a relatively wide spatial extension and low binding energy. In addition, a slow electron-hole recombination process is observed, with timescale on the order of 1.31 ns, which is even comparable with those of van der Waals (vdW) heterostructures. Further analysis reveals that the extremely long timescale for electron-hole recombination could be ascribed to the strong Coulomb screening effect as well as the small overlap of wavefunctions between electrons and holes. Our findings establish the build-in electric field as an effective factor to control the electron-hole recombination dynamics in TMD monolayers and facilitate their future applications in light detecting and harvesting.