ICFO - Institut de Ciències Fotòniques, Mediterranean Technology Park, Castelldefels (Barcelona) 08860, Spain.
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Nat Nanotechnol. 2015 May;10(5):437-43. doi: 10.1038/nnano.2015.54. Epub 2015 Apr 13.
Graphene is a promising material for ultrafast and broadband photodetection. Earlier studies have addressed the general operation of graphene-based photothermoelectric devices and the switching speed, which is limited by the charge carrier cooling time, on the order of picoseconds. However, the generation of the photovoltage could occur at a much faster timescale, as it is associated with the carrier heating time. Here, we measure the photovoltage generation time and find it to be faster than 50 fs. As a proof-of-principle application of this ultrafast photodetector, we use graphene to directly measure, electrically, the pulse duration of a sub-50 fs laser pulse. The observation that carrier heating is ultrafast suggests that energy from absorbed photons can be efficiently transferred to carrier heat. To study this, we examine the spectral response and find a constant spectral responsivity of between 500 and 1,500 nm. This is consistent with efficient electron heating. These results are promising for ultrafast femtosecond and broadband photodetector applications.
石墨烯是一种用于超快和宽带光探测的有前途的材料。早期的研究已经解决了基于石墨烯的光热电设备的一般操作问题，以及由载流子冷却时间决定的开关速度，其在皮秒量级。然而，光电压的产生可能发生在更快的时间尺度上，因为它与载流子加热时间有关。在这里，我们测量了光电压的产生时间，发现它快于 50fs。作为这个超快光探测器的原理验证应用，我们使用石墨烯直接测量了一个亚 50fs 激光脉冲的脉冲持续时间。载流子加热超快的这一观察结果表明，吸收光子的能量可以有效地转移到载流子热中。为了研究这一点，我们研究了光谱响应，并发现 500nm 到 1500nm 之间的光谱响应率保持不变。这与有效的电子加热一致。这些结果为超快飞秒和宽带光探测器的应用提供了希望。
