Organic-inorganic junctions formed on porous silicon: Isolation of a surface configuration primary to the luminescence mechanism

Organic-inorganic junctions were formed between porous silicon and various conjugated conducting polymers, poly(3-methylthiophene) and polypyrrole. Schottky type barriers were observed between the conducting polymers in their doped state and p and n-type porous silicon. In their undoped state the conducting polymers behave like p-type semiconductors. Consistent with this, ohmic contacts were observed between undoped conducting polymers and p-type porous silicon while rectifying behavior typical of a p-n junction was observed for conducting polymers deposited onto n-type porous silicon. During characterization of the porous silicon substrate, an investigation of the surface chemistry revealed a strong correspondence between solution pH and the luminescence intensity of porous silicon. Surface titration experiments were performed on p and n-type porous silicon and the results indicate that a monoprotic surface acid with a pKa between 3-4 is a primary component in the luminescence mechanism of porous silicon.