High pressure optical investigation of porous silicon

We have performed the first photoluminescence (PL) measurements under hydrostatic pressure up to 37 kbar at room temperature on several porous silicon (Si) samples fabricated under different etching conditions. A blue shift of the PL peak energy was observed in all samples from 0 to ∼20 kbar. Above ∼20 kbar, the PL peak energy appears to be constant or even to exhibit a small red shift with pressure in some samples. This pressure dependence of the PL peak energy of porous Si is different from the pressure induced red shift in the PL from the indirect band gap of the bulk Si crystal, or the red shift in the PL from amorphous Si. The intensity of the PL peaks showed a decrease with increasing pressure. We have also observed a red shift with time when a blue laser continuously illuminated the sample. These results on the pressure dependence of porous Si provide critical information for modeling and determining the electronic structure of porous silicon.