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

As an intrigued layered 2D semiconductor material, indium selenide (InSe) has attracted widespread attention due to its excellent properties. So far, the carrier dynamics of α-InSe and β-InSe are still lacking a comprehensive understanding, which is essential to enhancing the performance of InSe-based optoelectronic devices. In this study, we explored the ultrafast carrier dynamics in thin α-InSe and β-InSe transient absorption microscopy. For α-InSe 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-InSe, 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 InSe-based devices.