Impurity and topological surface states in porous silicon

We have developed a method, based on the effective mass approximation, for calculating electronic states in an arbitrarily shaped quantum nanostructure. Modelling the average porous silicon nanostructure with a deformed quantum wire, the calculated shallow impurity binding energies are in good agreement with surface photovoltage spectroscopy data. We have also studied a new type of surface carrier localization due to nanostructure surface geometrical irregularities. The implications of the existence of these trapping states are discussed for porous silicon.