Investigation of SiGe-heterostructure nanowires

Transport characterizations of wires obtained by electron beam lithography and etching of (100) Si/SiGe heterostructures with a high-mobility two-dimensional electron gas are reported. Depending on the wire width, two different regimes for the electrical transport are found. Wires with a width larger than ~200 nm exhibit metallic behaviour in the quasi-ballistic regime. The conductance dependence on the wire width reveals the presence of a depletion layer, ~100 nm thick, on each etched side of the wire. The wires of width smaller than 200 nm have very large resistance and two different behaviours. The first kind of wires exhibit a zero-current region, compatible with a Coulomb blockade effect involving multiple tunnel junctions or with a space-charge limited current. Other wires are insulating up to applied voltages larger than 5-6 V and their I-V characteristics can be fitted by the functional dependence of voltage-induced tunnelling of Fowler-Nordheim type.