Identification of excitons, trions and biexcitons in single-layer WS2

TL;DR

This study investigates the optical properties of single-layer WS2, demonstrating temperature-dependent exciton, trion, and biexciton emissions, and showing electrical control over excitonic states, with implications for optoelectronic applications.

Contribution

It provides the first detailed temperature-dependent photoluminescence analysis of excitonic complexes in single-layer WS2, including electrical tuning and identification of biexciton emission.

Findings

Neutral and charged excitons observed at all temperatures.

Electrical gating controls exciton-trion ratio.

Biexciton emission identified at high excitation and low temperature.

Abstract

Single-layer WS$_2$ is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS$_2$, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission.