Photo-excitation Cascade and Multiple Carrier Generation in Graphene

TL;DR

This paper demonstrates that in graphene, carrier-carrier scattering efficiently dominates energy relaxation after photoexcitation, leading to multiple hot electron generation, which enhances its potential for high-efficiency optoelectronic devices.

Contribution

It reveals that carrier-carrier scattering in graphene is highly efficient and surpasses phonon emission, enabling multiple hot carrier generation for energy conversion.

Findings

Carrier-carrier scattering dominates energy relaxation in graphene.

Multiple hot electrons are generated from a single photon.

Graphene's hot electrons can drive currents for optoelectronic applications.

Abstract

The conversion of light into free electron-hole pairs constitutes the key process in the fields of photodetection and photovoltaics. The efficiency of this process depends on the competition of different relaxation pathways and can be greatly enhanced when photoexcited carriers do not lose energy as heat, but instead transfer their excess energy into the production of additional electron-hole pairs via carrier-carrier scattering processes. Here we use Optical pump - Terahertz probe measurements to show that in graphene carrier-carrier scattering is unprecedentedly efficient and dominates the ultrafast energy relaxation of photoexcited carriers, prevailing over optical phonon emission in a wide range of photon wavelengths. Our results indicate that this leads to the production of secondary hot electrons, originating from the conduction band. Since hot electrons in graphene can drive currents, multiple hot carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.