Increased formation of trions and charged biexcitons by above-gap excitation in single-layer $WSe_2$

TL;DR

This study reveals that above-gap excitation in single-layer WSe2 significantly increases the formation of trions and charged biexcitons, providing new insights into excited state relaxation and carrier dynamics in 2D semiconductors.

Contribution

It demonstrates a distinct thermalization pathway at elevated excitation energies that enhances excitonic species formation in monolayer WSe2, advancing understanding of many-body effects.

Findings

Trions and charged biexcitons formation increased by up to 2x and 5x.

Elevated excitation energies induce a new thermalization pathway.

Power and temperature dependence elucidate the origin of enhancement.

Abstract

Two-dimensional semiconductors exhibit pronounced many-body effects and intense optical responses due to strong coulombic interactions. Consequently, subtle differences in photoexcitation conditions can strongly influence how the material dissipates energy during thermalization. Here, using multiple excitation spectroscopies, we show that a distinct thermalization pathway emerges at elevated excitation energies, enhancing the formation of trions and charged biexcitons in single-layer WSe2 by up to 2x and 5x, respectively. Power- and temperature-dependent measurements lend insight into the origin of the enhancement. These observations underscore the complexity of excited state relaxation in monolayer semiconductors, provide insight for the continued development of carrier thermalization models, and highlight the potential to precisely control excitonic yields and probe non-equilibrium dynamics in 2D semiconductors.