Photothermal Response in Dual-Gated Bilayer Graphene

The photovoltaic and bolometric photoresponse in gapped bilayer graphene was investigated by optical and transport measurements. A pulse coincidence technique at 1.5 mu m was used to measure the response times as a function of temperature. The bolometric and photovoltaic response times were found to be identical implying that the photovoltaic response is also governed by hot electron thermal relaxation. Response times of tau similar to 100 - 20 ps were found for temperatures from 3-100 K. Above 10 K, the relaxation time was observed to be tau = 25 +/- 5 ps, independent of temperature within noise.