Patent ID: 7977690

Claim:
A photovoltaic device comprising: a substrate; a plurality of nanowires on the substrate, wherein the plurality of nanowires attached to the substrate comprises a nanowire forest; a first doped semiconductor layer disposed conformally over the nanowire forest that conforms to, and has the same relative shape as, the nanowire forest, the first doped semiconductor layer comprising a first doping agent; a second doped semiconductor layer disposed conformally on the first doped semiconductor layer that conforms to, and has the same relative shape as, the nanowire forest, the second doped semiconductor layer comprising a second doping agent, wherein at least one of the first doped semiconductor layer and the second doped semiconductor layer comprises germanium, wherein the first doping agent comprises one of an n-type doping agent and a p-type doping agent and the second doping agent comprises a different one of the n-type doping agent and the p-type doping agent from the first doping agent, such that a p-n junction is formed over the nanowire forest, and wherein the substrate comprises a semiconductor material and is doped with one of the n-type doping agent and the p-type doping agent so as to be conductive; and a transparent electrode layer disposed over at least a portion of the second doped semiconductor layer.