All-porous silicon-coupled microcavities: Experiment versus theory

A detailed study of coupled porous silicon (PS) microcavities (PSM’s) is reported. The samples are investigated by room temperature photoluminescence and reflectivity. A splitting of the eigenmodes of the coupled cavity structure is observed, as well as a difference between the intensities of the cavity peaks related to mismatch between the two cavity thicknesses. The results are interpreted by a transfer matrix calculation of the optical response of the PSM, where the single PS layer is modeled by Si nanocrystals with a distribution of sizes. Comparison of calculations and experiments allows us to deduce the PS oscillator strength at the band gap. The oscillator strength per cell is found to be $f_{\mathrm{cell}}\sim 4\times {10}^{-5},$ i.e., small, which is consistent with the interpretation of the visible photoluminescence of PS as being due to indirect transitions of quantum confined electrons in Si nanocrystals.