Marcus Freitag, Tony Low, Fengnian Xia, Phaedon Avouris
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.
View original:
http://arxiv.org/abs/1202.5342
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