NH3 molecular doping of silicon nanowires grown along the , , , and  orientations
1 Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de Bellaterra, BellaterraBarcelona, 08193, Spain
2 Departament d’Enginyeria Electrònica, Universitat Autònoma de Barcelona, Campus de Bellaterra, Bellaterra, Barcelona, 08193, Spain
3 Instituto Politécnico Nacional, ESIME-Culhuacan, Av. Santa Ana 1000, México D.F., 04430, México
Nanoscale Research Letters 2012, 7:308 doi:10.1186/1556-276X-7-308Published: 18 June 2012
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 NH3 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 NH3 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 NH3 doping state, showing that the widening of the bandgap makes the molecular donor level deeper, thus more difficult to activate.