Impurity screening in silicon nanocrystals

The impurity screening in silicon nanocrystals is analyzed using a first-principles approach based on density functional theory. The electron density induced by a positively charged impurity is evaluated as a function of the nanocrystal size. From our calculations we found that the impurity is responsible for anelectron density accumulation around the impurity site, fully compensated by a positive charge accumulation at the surface(electron depletion). The results are sound and shed new light on the most recent findings in this field. On the basis of the present first-principles results, we propose a Thomas–Fermi model of the impurity screening in silicon nanocrystals. The model gives reliableestimations of the screening function, that well compares to recent ab-initio calculations.