Porous silicon grains in SiO2 matrix: Ultrafast photoluminescence and optical gain

We search for the presence of stimulated emission in samples of porous silicon embedded in the sol-gel derived SiO2 matrix. By modifying the etching conditions of the porous silicon using hydrogen peroxide, we decrease substantially the nanocrystal size and produce a significant blue shift of the PL emission. Femtosecond variable-stripe length experiments combined with the shifting-excited spot technique demonstrates positive optical gain (modal gain ∼25 cm−1) in the range 550-730 nm. Ultrafast photoluminescence dynamics indicates the origin of the stimulated emission as possibly due to recombination of excitonic states inside silicon nanocrystals.