Control of excitonic absorption by thickness variation in few-layer GaSe

TL;DR

This study demonstrates how varying the thickness of few-layer GaSe can control excitonic absorption, revealing a critical thickness below which excitonic transitions are suppressed, linked to fundamental band structure changes.

Contribution

It introduces a method to modulate optical absorption in GaSe by precise thickness control and links this to a fundamental band structure transformation.

Findings

Suppression of excitonic transitions below 8 layers

Identification of a band structure change to an inverted Mexican hat shape

Potential for thickness-based optoelectronic device tuning

Abstract

We control the thickness of GaSe on the level of individual layers and study the corresponding optical absorption via highly sensitive differential transmission measurements. Suppression of excitonic transitions is observed when the number of layers is smaller than a critical value of 8. Through ab-initio modelling we are able to link this behavior to a fundamental change in the band structure that leads to the formation of a valence band shaped as an inverted Mexican hat in thin GaSe. The thickness-controlled modulation of the optical properties provides attractive resources for the development of functional optoelectronic devices based on a single material.