NH(3) molecular doping of silicon nanowires grown along the [112], [110], [001], and [111] orientations

The possibility that an adsorbed molecule could provide shallow electronic states that could be thermally excited has received less attention than substitutional impurities and could potentially have a high impact in the doping of silicon nanowires (SiNWs). We show that molecular-based ex-situ doping, where NH(3) is adsorbed at the sidewall of the SiNW, can be an alternative path to n-type doping. By means of first-principle electronic structure calculations, we show that NH(3) is a shallow donor regardless of the growth orientation of the SiNWs. Also, we discuss quantum confinement and its relation with the depth of the NH(3) doping state, showing that the widening of the bandgap makes the molecular donor level deeper, thus more difficult to activate.