Porous silicon formation: A quantum wire effect

Porous silicon layers grown on nondegenerated p-type silicon electrodes in hydrofluoric acid electrolytes are translucent for visible light, which is equivalent to an increased band gap compared to bulk silicon. It will be shown that a two-dimensional quantum confinement (quantum wire) in the very narrow walls between the pores not only explains the change in band-gap energy but may also be the key to better understanding the dissolution mechanism that leads to porous silicon formation.