Temperature effects in contacts between a metal and a semiconductor nanowire near the degenerate doping

We have investigated the nonlinear conductance in diffusion-doped Si:GaAs nanowires contacted by patterned metal films in a wide range of temperaturesT. The wire resistanceR_Wand the zero bias resistanceR_C, dominated by the contacts, exhibit very different responses to temperature changes. WhileR_Wshows almost no dependence onT,R_Cvaries by several orders of magnitude as the devices are cooled from room temperature toT = 5 K. We develop a model that employs a sharp donor level very low in the GaAs conduction band and show that our observations are consistent with the model predictions. We then demonstrate that such measurements can be used to estimate carrier properties in nanostructured semiconductors and obtain an estimate forN_D, the doping density in our samples. We also discuss the effects of surface states and dielectric confinement on carrier density in semiconductor nanowires.