A novel method to fabricate silicon nanowire p-n junctions by a combination of ion implantation and in-situ doping

We demonstrate that axial p-n junction silicon nanowire (Si NW) diodes can be fabricated over a large area (5` Si wafer) by applying two existing doping techniques in succession. We doped the lower segments of the NWs p-type, in situ during growth with boron by molecular beam epitaxy, and the upper segments n-type, ex situ with phosphorus by ion implantation and subsequent rapid thermal annealing. No structural defects were observed in the NWs by transmission electron microscopy after implantation and rapid thermal annealing. Electrical measurements of individual NWs showed excellent diode characteristics with ideality factors higher than 2. Such high ideality factor can be attributed to the surface-states assisted recombination-generation in the depletion region of the p-n junction. The combined doping technique reduces the unwanted lateral doping and the extended overlapping region between n and p-doped segments in the NWs which is common in pure in situ doping. Our fabrication technique can be easily applied to form arrays of Si NW diodes for solar cells and other applications.