▎ 摘　　要

We report photoresponse observations in epitaxial graphene (EG) devices with asymmetric metals (Au, Al) contacted in planar Au/EG/Al device format. The transient photocurrent measurements on the zero-bias device show photocurrent maxima at the Au/EG contact and minima at the EG/Al contact. This observed significant difference between the two types of junctions is responsible for the overall efficient device photoresponse. We have also found that the number of EG layers influences the photocurrent magnitude and response time regardless of incident photon energy or intensity. An external photoresponsivity (or efficiency) of similar to 31.3 mA W-1 is achieved with a biased Au/EG/Al photodetector at excitation wavelength of 632.8 nm. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3692107]