Ultrafast electrons dynamics reveal the high potential of InSe for hot carrier optoelectronics

TL;DR

This study investigates hot carrier dynamics in InSe using 2PPE, revealing rapid relaxation processes and potential for high-speed optoelectronic devices like photodiodes and oscillators based on layered chalcogenides.

Contribution

The paper provides experimental and theoretical insights into hot carrier relaxation in InSe, highlighting its potential for ultrafast optoelectronic applications.

Findings

Hot carriers thermalize to degenerate states with the $ar M$ valley.

Electronic cooling is governed by Fröhlich phonon coupling.

InSe can support hot carrier transport over micrometer scales.

Abstract

We monitor the dynamics of hot carriers in InSe by means of two photons photoelectron spectroscopy (2PPE). The electrons excited by photons of 3.12 eV experience a manifold relaxation. First, they thermalize to the electronic states degenerate with the $\bar M$ valley. Subsequently, the electronic cooling is dictated by Fr\"ohlich coupling with phonons of small momentum transfer. Ab-initio calculations predict cooling rates that are in good agreement with the observed dynamics. We argue that electrons accumulating in states degenerate with the $\bar M$ valley could travel through a multilayer flake of InSe with lateral size of 1 micrometer. The hot carriers pave a viable route to the realization of below-bandgap photodiodes and Gunn oscillators. Our results indicate that these technologies may find a natural implementation in future devices based on layered chalcogenides.