Tunable Carrier Multiplication and Cooling in Graphene

TL;DR

This study demonstrates that doping levels in graphene can be tuned to control hot carrier multiplication and cooling dynamics, revealing potential for optimized optoelectronic applications.

Contribution

It provides the first detailed comparison of ultrafast carrier dynamics in differently doped graphene using time- and angle-resolved photoemission spectroscopy.

Findings

Stronger ($n$-)doping leads to carrier multiplication factors over 3.

Faster phonon-mediated cooling observed in more heavily doped graphene.

Doping level tuning effectively manipulates graphene's ultrafast electronic response.

Abstract

Time- and angle-resolved photoemission measurements on two doped graphene samples displaying different doping levels reveal remarkable differences in the ultrafast dynamics of the hot carriers in the Dirac cone. In the more strongly ($n$-)doped graphene, we observe larger carrier multiplication factors ($>$ 3) and a significantly faster phonon-mediated cooling of the carriers back to equilibrium compared to in the less ($p$-)doped graphene. These results suggest that a careful tuning of the doping level allows for an effective manipulation of graphene's dynamical response to a photoexcitation.