Photoconductivity of biased graphene

TL;DR

This study investigates the intrinsic photoresponse of biased homogeneous graphene, revealing that photovoltaic and bolometric effects dominate due to hot carrier dynamics, with hot electrons primarily driving the photovoltaic response near the Dirac point.

Contribution

It demonstrates the intrinsic photoresponse mechanisms in biased homogeneous graphene, emphasizing hot electron effects over thermoelectric effects, and clarifies the roles of photovoltaic and bolometric responses.

Findings

Photocurrent polarity reverses with gate voltage.

Hot electrons reach temperatures much higher than phonons.

Photovoltaic response is driven by hot electron dynamics.

Abstract

Graphene is a promising candidate for optoelectronic applications such as photodetectors, terahertz imagers, and plasmonic devices. The origin of photoresponse in graphene junctions has been studied extensively and is attributed to either thermoelectric or photovoltaic effects. In addition, hot carrier transport and carrier multiplication are thought to play an important role. Here we report the intrinsic photoresponse in biased but otherwise homogeneous graphene. In this classic photoconductivity experiment, the thermoelectric effects are insignificant. Instead, the photovoltaic and a photo-induced bolometric effect dominate the photoresponse due to hot photocarrier generation and subsequent lattice heating through electron-phonon cooling channels respectively. The measured photocurrent displays polarity reversal as it alternates between these two mechanisms in a backgate voltage sweep. Our analysis yields elevated electron and phonon temperatures, with the former an order higher than the latter, confirming that hot electrons drive the photovoltaic response of homogeneous graphene near the Dirac point.