Electronic level scheme in boron- and phosphorus-doped silicon nanowires

We report the first observation of the electronic level scheme in boron (B)- and phosphorus (P)-doped nanowires (NWs). The NWs' morphology dramatically depends on the doping impurity while a few deep electronic levels appear in both kinds of nanowires, independently of the doping type. We demonstrate that the doping impurities induce the same shallow levels as in bulk silicon. The presence of two donor levels in the lower half-bandgap is also revealed. In both kinds of NWs, B- and P-doped, the donor level (0/+) at E(v) + 0.36 eV of the gold-hydrogen complex is observed. This means that the gold diffusion from the NW tip introduces an electronically active level, which might negatively affects the electrical characteristics of the NWs. In P-doped NWs, we observed a further donor level at 0.26 eV above the valence band due to the phosphorus-vacancy pairs, the E-center, well-known in bulk silicon. These findings seriously question both diffusion modeling of impurities in NWs and the technological aspects arising from this.