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 nanostructnr e. Modelling the average porous silicon nanostructure with a deformed quant um wire, the calculated shallow impur ity binding energies are in good agre ement with surface photovoltage spectroscopy data. We have also studied a n ew type of surface carrier. localization clue to nanostructure: surface geo metrical irregularities. The implications of the existence or these: trappi ng states are discussed for porous silicon.