Photoluminescence mechanisms in porous silicon

It is found that the lateral etching rate increases with increasing intensities of photo-irradiation during electrochemical etching of porous silicon until its bandgap becomes larger than the photon energies. The corresponding photoluminescence peak energies blueshift then saturate. These suggest that the photoluminescence spectra of the as fabricated samples are controlled by the quantum size effect. On the other hand, It is shown that the transitions between the oxide levels produce the photoluminescence with the peak position at about 1.7 eV, because the photoluminescence peak energies of the as fabricated samples ranging from 1.45 to 1.92 eV shift toward 1.7 eV after the samples axe oxidized in air for a period of time. Both the quantum size effect and the oxide related transitions should be attributed to the photoluminescence mechanisms.