Coulomb blockade in strained-Si nanowires on leaky virtual substrates

Nanowires fabricated from a modulation-doped Si/Si_0.7Ge_0.3 heterostructure grown on a virtual substrate can exhibit Coulomb blockade due to single-electron charging of multiple islands. A non-blockaded behaviour in some wires is attributed to a combination of incomplete tunnel barrier formation and leakage currents. The leakage manifests itself in the form of a B² dependence in magnetoresistance measurements. It is found that the leakage arises mainly from the substrate. In some narrow nanowires at very low temperatures, the leakage is negligible and electronic transport along the wires can be explained using the classical Coulomb blockade theory. It is believed that threading dislocations are responsible for the formation of Coulomb islands in the wires. The islands' sizes and the number of tunnel barriers separating the islands agree well with the geometrical dimensions of the fabricated wires.