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(cell)similar to 4x10(-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. [S0163-1829(98)02139-0].