11 research outputs found
Photoconductivity of biased graphene
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
Thermal infrared emission reveals the Dirac point movement in biased graphene
Graphene is a 2-dimensional material with high carrier mobility and thermal
conductivity, suitable for high-speed electronics. Conduction and valence bands
touch at the Dirac point. The absorptivity of single-layer graphene is 2.3%,
nearly independent of wavelength. Here we investigate the thermal radiation
from biased graphene transistors. We find that the emission spectrum of
single-layer graphene follows that of a grey body with constant emissivity (1.6
\pm 0.8)%. Most importantly, we can extract the temperature distribution in the
ambipolar graphene channel, as confirmed by Stokes/anti-Stokes measurements.
The biased graphene exhibits a temperature maximum whose location can be
controlled by the gate voltage. We show that this peak in temperature reveals
the spatial location of the minimum in carrier density, i.e. the Dirac point.Comment: Accepted in principle at Nature Nanotechnolog