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 ∼1G0 to ∼10−6G0, where G0 is the quantum unit of conductance. The conductance histogram plotted against log(G∕G0) reveals peaklike structures for G>10−3G0, but becomes featureless for 10−6G0<G<10−3G0. 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 10−4G0. 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 ΔL and found a quadratic dependence of log(G∕G0) on ΔL, suggesting the localization of carriers in disordered Si NWs.