Understanding and Mitigating the Degradation of Optical Emission from Exfoliated Ga2Se2

Gallium selenide (Ga₂Se₂) is a promising 2D material for use in both classical and quantum photonic device technologies because it transitions to a direct bandgap as a function of both increasing film thickness and applied strain. However, the optical emission from thin exfoliated Ga₂Se₂ films has been reported to degrade rapidly, which would severely limit its usefulness for optoelectronic applications. We perform a systematic time-dependent study of the intensity of photoluminescence emitted from exfoliated Ga₂Se₂ as a function of both the sample preparation and storage conditions. We find that the degradation of optical properties is substantially slower than previously reported. We further find that the degradation is a surface effect that begins upon transient exposure to air and that the degradation cannot be mitigated by any reasonable sample storage conditions. Finally, we show that the optical degradation can be eliminated by utilizing hexagonal boron nitride (h-BN) encapsulation in a glovebox to protect the Ga₂Se₂ from even momentary air exposure.