Evidence for extraction of photoexcited hot carriers from graphene.

We report evidence of nonequilibrium hot carrier extraction from graphene by gate-dependent photocurrent study. Scanning photocurrent excited by femtosecond pulse laser shows unusual gate dependence compared with continuous wave (CW) laser excitation. Power dependence studies further confirm that the photocarriers extracted at the metal/graphene contact are nonequilibrium hot carriers. Hot carrier extraction is found to be most efficient near the Dirac point where carrier lifetime reaches a maximum. These observations not only provide evidence of hot carrier extraction from graphene but also open the door for graphene-based hot carrier optoelectronics.