Conductance of Si nanowires formed by breaking Si-Si junctions

We have fabricated Si nanowires (NWs) by breaking Si-Si tip-sample junctions and studied their conductance for both p-n and p-p-type junctions at room temperature. Upon breaking the junction by retracting the Si tip from the Si clean surface, the conductance decreases by orders of magnitude from similar to 1G(0) to similar to 10(-6)G(0), where G(0) is the quantum unit of conductance. The conductance histogram plotted against log(G/G(0)) reveals peaklike structures for G > 10(-3)G(0), but becomes featureless for 10(-6)G(0)< G < 10(-3)G(0). In this low-conductance region, the histogram shows strong dependence on bias polarity and doping; the p-type-tip-n-type-sample junctions under positive sample biases yield large intensity in the histogram, while the same junctions under the opposite bias polarity and the p-p junctions under both bias polarities show small intensity below 10(-4)G(0). This observation suggests that longer and thinner Si NWs can be preferably formed in the reversely biased p-n Si junctions. We also investigated how the conductance of Si NWs varies with the tip displacement Delta L and found a quadratic dependence of log(G/G(0)) on Delta L, suggesting the localization of carriers in disordered Si NWs. (c) 2007 American Institute of Physics.