Quenching the photoluminescence from Si nanocrystals of smaller sizes in dense ensembles due to migration processes

We investigate both experimentally and theoretically the role of migration effects in a relaxation of the ensemble of Si crystallites formed in multilayer SiOx/SiO2 nano-periodic structure with annealing. Photoluminescence spectrum of the multilayer ensemble turns out to be strongly redshifted and narrowed related to its position and width expected from the size distribution of the nanocrystals. Based on the concept of “quantum confinement” we have performed a computer experiment on the ensemble relaxation with taking the migration of electrons, holes, and excitons into account for the ensemble having the size distribution and nanocrystals׳ density similar to those in the experimental sample. This model allows us to calculate the photoluminescence spectrum that agrees well with the one observed experimentally. It was shown experimentally and theoretically that in a dense ensemble, the migration quenches the luminescence of Si nanocrystals whose diameters are, in fact, less than the average nanocrystal diameter in the ensemble. This explains the above mentioned features of the measured spectrum.