Charge Transport Characteristics in Boron-Doped Silicon Nanowires

We report the charge transport and inferred surface depletion characteristics of silicon nanowires (Si NWs) with diameters of 90-170 nm after boron doping to 8 times 10¹⁷ and 4 times 10¹⁹ cm^-3 by a proximity diffusion doping technique. Four-probe current-voltage measurements were performed to obtain the NW resistivity, and the electrically active dopant concentration and surface oxide charge density were extracted by varying the NW diameter. The Ti/Au to Si NW contact resistance and specific contact resistivity were also obtained, and specific contact resistivities as low as 2 times 10^-5 Omega middot cm² were achieved. The derived parameters for these ex situ boron-doped Si NWs agree reasonably well with the expected characteristics and earlier reported results for in situ boron-doped Si NWs. Interface charge creates a surface depletion region in p-type Si NWs, which decreases the conducting area of the NW. This effect increases the NW resistance and becomes increasingly significant with decreasing dopant concentration and NW diameter. A simple method is presented to estimate the relative influence of surface charge density on electrical transport in NWs for this case.