Surface Dangling Bond-Mediated Molecules Doping of Germanium Nanowires

We report on the controllable doping of germanium nanowires (GeNWs) via selective molecule adsorption on the surface dangling bond. The GeNWs investigated are fabricated by evaporating pure germanium powder. Electron spin resonance analysis shows the presence of a surface dangling bond with g value of 2.023 and a spin density of C-spin = 2.47 x 10(13) mg(-1). The as-prepared undoped GeNW exhibits typical p-type conduction behavior in air but n-type electrical characteristics in ammonia atmosphere. Significantly, the conductance, carrier mobility, and concentrations are found to be highly dependent on vacuum and ammonia gas pressures. Such an ambient effect could be explained by a surface dangling bond-mediated molecule doping model, according to which an acceptor or donor level is formed by water or ammonia adsorption, respectively. The generality of the above results suggests that surface dangling bond-mediated molecule doping may be applicable to modulation of the electrical characteristics of other semiconductor nanostructures.