We investigated Si nanowires (SiNWs) fabricated by wet etching and chemical vapor deposition (CVD), and core-shell structures, formed by depositing silicon layers around the SiNWs, with respect to their crystallinity, the doping level, and the influence of surface passivation on carrier lifetime. The effects expected to be critical to improve the performance of nanowire-based solar cells are discussed. ©2010 IEEE.