Microsecond Valley Lifetime of Defect-Bound Excitons in Monolayer WSe$_2$

TL;DR

This study demonstrates that electron-beam irradiation can create defect-bound excitons in monolayer WSe2 with exceptionally long recombination and valley lifetimes, enabling advanced optoelectronic applications.

Contribution

It introduces a simple electron irradiation method to engineer defect-bound excitons with long lifetimes in monolayer WSe2, advancing control over 2D material optical properties.

Findings

Defect-bound excitons have a recombination lifetime approaching 200 ns.

Valley lifetime exceeds 1 microsecond.

Electron irradiation effectively introduces chalcogen vacancy defects.

Abstract

In atomically thin two-dimensional semiconductors such as transition metal dichalcogenides (TMDs), controlling the density and type of defects promises to be an effective approach for engineering light-matter interactions. We demonstrate that electron-beam irradiation is a simple tool for selectively introducing defect-bound exciton states associated with chalcogen vacancies in TMDs. Our first-principles calculations and time-resolved spectroscopy measurements of monolayer WSe2 reveal that these defect-bound excitons exhibit exceptional optical properties including a recombination lifetime approaching 200 ns and a valley lifetime longer than 1 $\mu$s. The ability to engineer the crystal lattice through electron irradiation provides a new approach for tailoring the optical response of TMDs for photonics, quantum optics, and valleytronics applications.