Molecular Doping and Subsurface Dopant Reactivation in Si Nanowires

Impurity doping in semiconductor nanowires, while increasingly well understood, is not yet controllable at a satisfactory degree. The large surface-to-volume area of these systems, however, suggests that adsorption of the appropriate molecular complexes on the wire sidewalls could be a viable alternative to conventional impurity doping. We perform first-principles electronic structure calculations to assess the possibility of n- and p-type doping of Si nanowires by exposure to NH3 and NO2. Besides providing a full rationalization of the experimental results recently obtained in mesoporous Si, our calculations show that while NH3 is a shallow donor, NO2 yields p-doping only when passive surface segregated B atoms are present.