Band-offset driven efficiency of the doping of SiGe core-shell nanowires

Impurity doping of semiconducting nanowireshas been predicted to become increasingly inefficient as thewire diameter is reduced, because impurity states get deeperdue to quantum and dielectric confinement. We show thatefficient n- and p-type doping can be achieved in SiGe coreshellnanowires as thin as 2 nm, taking advantage of the bandoffset at the Si/Ge interface. A one-dimensional electron(hole) gas is created at the band-edge and the carrier densityis uniquely controlled by the impurity concentration with noneed of thermal activation. Additionally, SiGe core-shellnanowires provide naturally the separation between thedifferent types of carriers, electron and holes, and are ideallysuited for photovoltaic applications.