Oxidation dynamics of ultrathin GaSe probed through Raman spectroscopy

TL;DR

This study investigates the oxidation process of ultrathin GaSe under ambient conditions using Raman spectroscopy, revealing rapid degradation due to photo-oxidation triggered by oxygen, humidity, and illumination, which impacts its optoelectronic applications.

Contribution

It provides the first detailed analysis of GaSe oxidation dynamics under realistic conditions, highlighting the risks of optical measurement and the mechanisms involved.

Findings

Rapid decrease in Raman signal and luminescence with exposure

Identification of oxidation products Ga2Se3, Ga2O3, and selenium

Photo-oxidation requires oxygen, humidity, and illumination

Abstract

Gallium selenide (GaSe) is a 2D material with a thickness-dependent gap, strong non-linear optical coefficients and uncommon interband optical selection rules, making it interesting for optoelectronic and spintronic applications. In this work, we monitor the oxidation dynamics of GaSe with thicknesses ranging from 10 to 200 nm using Raman spectroscopy. In ambient temperature and humidity conditions, the intensity of all Raman modes and the luminescence decrease rapidly with moderate exposure to above-gap illumination. Concurrently, several oxidation products appear in the Raman spectra: Ga$_2$Se$_3$, Ga$_2$O$_3$ and amorphous and crystalline selenium. We find that no safe measurement power exists for optical measurements on ultrathin GaSe in ambient conditions. We demonstrate that the simultaneous presence of oxygen, humidity, and above-gap illumination is required to activate this photo-oxidation process, which is attributed to the transfer of photo-generated charge carriers towards aqueous oxygen at the sample surface, generating highly reactive superoxide anions that rapidly degrade the sample and quench the optical response of the material.