Room temperature observation of biexcitons in exfoliated WS2 monolayers

TL;DR

This study demonstrates the stable existence of biexcitons in exfoliated WS2 monolayers at room temperature, with a binding energy of 65-70 meV, advancing potential optoelectronic applications.

Contribution

It reports the first observation of biexcitons in WS2 monolayers at room temperature using temperature and power dependent photoluminescence measurements.

Findings

Biexcitons observed from 78 K to room temperature.

Biexciton binding energy estimated at 65-70 meV.

Superlinear PL intensity indicates biexciton formation.

Abstract

Single layers of WS2 are direct gap semiconductors with high photoluminescence (PL) yield holding great promise for emerging applications in optoelectronics. The spatial confinement in a 2D monolayer together with the weak dielectric screening lead to huge binding energies for the neutral excitons as well as other excitonic complexes, such as trions and biexcitons whose binding energies scale accordingly. Here, we report on the existence of biexcitons in mechanically exfoliated WS2 flakes from 78 K up to room temperature. Performing temperature and power dependent PL measurements, we identify the biexciton emission channel through the superlinear behavior of the integrated PL intensity as a function of the excitation power density. On the contrary, neutral and charged excitons show a linear to sublinear dependence in the whole temperature range. From the energy difference between the emission channels of the biexciton and neutral exciton, a biexciton binding energy of 65-70 meV is determined.