  We present the optoelectronic characterization of two graphene/silicon
Schottky junctions, fabricated by transferring CVD-graphene on flat and
nanotip-patterned n-Si substrates, respectively. We demonstrate record photo
responsivity, exceeding 2.5 A/W under white light, which we attribute to the
contribution of charges photogenerated in the surrounding region of the flat
junction or to the internal gain by impact ionization caused by the enhanced
field on the nanotips.
