Doping efficiency in freestanding silicon nanocrystals from the gas phase: Phosphorus incorporation and defect-induced compensation

Electron paramagnetic resonance (EPR) and secondary-ion mass spectroscopy have been used to quantitatively investigate the phosphorus doping of freestanding silicon nanocrystals (Si-NCs) in a wide range of diameters. It is found that both the atomic phosphorus incorporation efficiency of 100% and its segregation to the surface region during growth by our gas-phase method are independent of the nominal doping concentration and the Si-NC size. EPR data show that the concentration of electrically active substitutional P falls below the atomic P concentration by about 1 order of magnitude for Si-NC with diameters larger than 12 nm. Using a quantitative statistical model, charge compensation by Si dangling bonds is shown to be the reason for this difference. For smaller Si-NCs, a further strong drop of the concentration of paramagnetic donors is observed.