Fig. 2

Photocurrent transportation in graphene p-i-n junction. a Scanning photocurrent microscopy across the silicon p-i-n junction with (red circles) and without (blue open squares) graphene, under 532 nm 797 nW pump excitation without gate nor external bias. Solid/dashed lines are Gaussian/exponential fits. The peak position of the photocurrent profile in the intrinsic region is determined by the mean free path of minority carriers. b Surface conductivity scan across the G–Si junction, with the position of the Raman G peak of graphene and substrate silicon doping level. The electrostatically formed homojunction in graphene is achieved through directly contacting to a silicon p-i-n junction. c The calculated built-in electric field along the p-i-n junction (E_x), for monolithic silicon device (dashed blue curve) and graphene supported by silicon p-i-n junction. d Current–gate voltage characteristics in dark (dotted black curve), as the laser spot on intrinsic silicon without (dashed blue curve) and with graphene coverage (red solid curve). Inset: the photocurrent map across the G–Si p-i-n junction at 2.5 V gate voltage. The convoluted profile (empty circles are experiments, and the red curve is Gaussian fit) can be decomposed into graphene (dashed red curve) and silicon (blue dashed curve) contributions