AN EXTENDED QUANTUM MODEL FOR POROUS SILICON FORMATION

Porous silicon formed by anodization of a p-type silicon substrate is characterized by a distribution of crystallites with diameters smaller than about 100 Angstrom. The corresponding size distributions obtaine d from Raman measurements show distinct peaks which are explained for the first time by the tunneling of holes through crystallite barriers during the formation process of porous silicon. The theoretical descri ption is based on quantum mechanical calculations of the tunneling pro bability of the holes through small crystallites into the electrolyte. This tunneling probability shows oscillations as a function of crysta llite size which are comparable to the structures observed in the size distributions, The calculations presented provide a deeper understand ing of these size distributions and of the basic formation mechanism o f porous silicon.