Screening in Semiconductor Nanocrystallites and Its Consequences for Porous Silicon

Consequences of the modified dielectric properties of semiconductor crystallites are explored. The notion and usefulness of an effective dielectric constant are analyzed using a self-consistent linear screening calculation. The binding energy of hydrogenic impurities is defined and calculated, and it is shown why these are always ionized in porous silicon. Self-energy terms associated with the surface polarization charge are discussed in the context of Coulomb charging effects. Their contribution to exciton binding energies is also determined. Consequences of charging effects on carrier injection in porous silicon are finally considered and shown to be important.