The resistivity and the mobility of Carbon doped GaAs nanowires have been studied for different doping concentrations. Surface effects have been evaluated by comparing upassivated with passivated nanowires. We directly see the influence of the surface: the pinning of the Fermi level and the consequent existence of a depletion region lead to an increase of the mobility up to 30 cm^2/(V*s) for doping concentrations lower than 3*10^18 cm^-3. Electron beam induced current measurements show that the minority carrier diffusion path can be as high as 190 nm for passivated nanowires.
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