# Direct observation of giant binding energy modulation of exciton complexes in monolayer MoSe$_2$

## TL;DR

This study demonstrates the significant modulation of exciton binding energies in monolayer MoSe$_2$ through dielectric environment changes, revealing a complex interplay with bandgap renormalization and potential for novel optoelectronic devices.

## Contribution

It provides the first direct experimental evidence of giant binding energy modulation of exciton complexes in monolayer TMDs due to dielectric screening effects.

## Key findings

- Exciton binding energy can be modulated by over 58% in monolayer MoSe$_2$.
- The 1s exciton peak remains unchanged despite dielectric screening.
- Bandgap renormalization reduces the quasi-particle bandgap by approximately 248 meV.

## Abstract

Screening due to surrounding dielectric medium reshapes the electron-hole interaction potential and plays a pivotal role in deciding the binding energies of strongly bound exciton complexes in quantum confined monolayers of transition metal dichalcogenides (TMDs). However, owing to strong quasi-particle bandgap renormalization in such systems, a direct quantification of estimated shifts in binding energy in different dielectric media remains elusive using optical studies. In this work, by changing the dielectric environment, we show a conspicuous photoluminescence (PL) peak shift at low temperature for higher energy excitons (2s, 3s, 4s, 5s) in monolayer MoSe$_2$, while the 1s exciton peak position remains unaltered - a direct evidence of varying compensation between screening induced exciton binding energy modulation and quasi-particle bandgap renormalization. The estimated modulation of binding energy for the 1s exciton is found to be 58.6% (70.5% for 2s, 78.9% for 3s, 85% for 4s) by coating an Al$_2$O$_3$ layer on top, while the corresponding reduction in quasi-particle bandgap is estimated to be 248 meV. Such a direct evidence of large tunability of the binding energy of exciton complexes as well as the bandgap in monolayer TMDs holds promise of novel device applications.

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Source: https://tomesphere.com/paper/1703.07057