Abstrakt
The absolute photoluminescence (PL) quantum yield (QY) of multilayers of Silicon nanocrystals (SiNCs) separated by SiO2 barriers were thoroughly studied as function of the barrier thickness, excitation wavelength, and temperature. By mastering the plasma-enhanced chemical vapor deposition growth, we produce a series of samples with the same size-distribution of SiNCs but variable interlayer barrier distance.
These samples enable us to clearly demonstrate that the increase of barrier thickness from similar to 1 to larger than 2 nm induces doubling of the PL QY value, which corresponds to the change of number of close neighbors in the hcp structure. The temperature dependence of PL QY suggests that the PL QY changes are due to a thermally activated transport of excitation into non-radiative centers in dark NCs or in the matrix.
We estimate that dark NCs represent about 68% of the ensemble of NCs. The PL QY excitation spectra show no significant changes upon changing the barrier thickness and no clear carrier multiplication effects.
The dominant effect is the gradual decrease of the PL QY with increasing excitation photon energy. (C) 2014 AIP Publishing LLC.