Distinct ultrafast carrier dynamics of α-In2Se3 and β-In2Se3: contributions from band filling and bandgap renormalization

Abstract

As an intrigued layered 2D semiconductor material, indium selenide (In₂Se₃) has attracted widespread attention due to its excellent properties. So far, the carrier dynamics of α-In₂Se₃ and β-In₂Se₃ are still lacking a comprehensive understanding, which is essential to enhancing the performance of In₂Se₃-based optoelectronic devices. In this study, we explored the ultrafast carrier dynamics in thin α-In₂Se₃ and β-In₂Se₃via transient absorption microscopy. For α-In₂Se₃ with a narrower bandgap, band filling and bandgap renormalization jointly governed the time evolution of the differential reflectivity signal, whose magnitude and sign at different delays were determined by the weights between the band filling and bandgap renormalization, depending on the carrier density. For β-In₂Se₃, whose bandgap is close to the probe photon energy, only positive differential reflectivity was detected, which was attributed to strong band filling effect. In both materials, the lifetime decreased and the relative amplitude of the Auger process increased, when the pump fluence was increased. These findings could provide further insights into the optical and optoelectronic properties of In₂Se₃-based devices.