  The design of efficient graphene-silicon (GSi) Schottky junction
photodetectors requires detailed understanding of the spatial origin of the
photoresponse. Scanning-photocurrent-microscopy (SPM) studies have been carried
out in the visible wavelengths regions only, in which the response due to
silicon is dominant. Here we present comparative SPM studies in the visible
($\lambda$ = 633nm) and infrared ($\lambda$ = 1550nm) wavelength regions for a
number of GSi Schottky junction photodetector architectures, revealing the
photoresponse mechanisms for silicon and graphene dominated responses,
respectively, and demonstrating the influence of electrostatics on the device
performance. Local electric field enhancement at the graphene edges leads to a
more than ten-fold increased photoresponse compared to the bulk of the
graphene-silicon junction. Intentional design and patterning of such graphene
edges is demonstrated as an efficient strategy to increase the overall
photoresponse of the devices. Complementary simulations and modeling illuminate
observed effects and highlight the importance of considering graphene's shape
and pattern and device geometry in the device design.
