First-principles study of doped Si and Ge nanowires

Using density functional theory we calculate the formation energies for B and P doped Si and Ge nanowires which are oriented in the [1 1 0] direction. First the preferential position for the dopants is calculated in fully passivated nanowires. It is found that the dopants prefer the edge or near edge positions. Further we show that a dangling bond has a large influence on these formation energies. When a dangling bond is present, P dopants will segregate to the edge of the wire, thereby trapping its additional electron and thus lowering the conductance. For B dopants this effect is smaller.