Effect of coalescence and of the character of the initial oxide on the photoluminescence of ion-synthesized Si nanocrystals in SiO2

The photoluminescence intensity (PLI) related to Si nanocrystals in a SiO₂: nc-Si system synthesized by ion implantation is studied experimentally and theoretically as a function of the Si+ ion dose at various annealing temperatures T_ann (1000–1200°C). The dose corresponding to the maximum PLI is found to decrease with increasing T_ann. These data are explained in terms of a model taking into account the coalescence of neighboring nanocrystals and the dependence of the probability of radiative recombination of quantum dots on their size. It is found that, when silicon oxide is grown in a wet atmosphere, the photoluminescence spectrum contains an additional band (near 850 nm), which is related to shells around the nanocrystals. This band weakens abrupily after high-temperature annealing in an oxidizing atmosphere (air).