Effect of particle size on the photoluminescence from hydrogen passivated Si nanocrystals in SiO2

Abstract

The effect of hydrogen passivation on the photoluminescence from Si nanocrystals prepared in SiO2 by ion implantation and annealing is examined as a function of nanocrystal size (implant fluence). Passivation is shown to produce a significant increase in emission intensities as well as a redshift of spectra, both of which increase with increasing fluence. These results are shown to be consistent with a model in which larger nanocrystals are assumed to contain more nonradiative defects (i.e., the defect concentration is assumed to be proportional to the nanocrystal surface area or volume). Since this results in a smaller fraction of larger nanocrystals contributing to the initial luminescence, emission spectra are initially blueshifted relative to that that might be expected from the physical nanocrystal size distribution. The contribution from larger crystallites is then disproportionately increased by passivation resulting in the observed redshift.

Optical and structural properties of Si nanocrystals produced by Si hot implantation

“…10,[13][14][15] However, in all the previous works the implantation has been performed at room temperature ͑RT͒ and only one PL band centered at 780 nm was observed, in agreement with results obtained using the other techniques mentioned ͑CVD, MBE, etc͒.…”

“…Larger Si NCs having longer radiative lifetimes 25 are also more likely to contain nonradiative recombination centers. 14 Concerning the annealing time dependence of the 1000 nm PL band, it shows a significant PL peak redshift with increasing annealing time ͑up to 6 h͒, followed by saturation-see Fig. 6͑b͒.…”

From amorphous to crystalline silicon nanoclusters: structural effects on exciton properties

“…This is evidence of H passivation of the remaining Si-dbs in the samples. As will be shown in section 3.3, increases of the PL intensity by comparable factors are observed, as is expected from the H passivation given that dbs act as efficient non-radiative recombination centers in both amorphous Si [27] and Si nanostructures [6,9,17,24,[29][30][31][32][33][34][35].…”

Photoluminescence behavior of Si nanocrystals as a function of the implantation temperature and excitation power density

“…For instance, it is well known that passivation of nonradiative interface states enhances the photoluminescence properties of the Si NC without changing the crystallite size. 5,6 On the other hand, an increase in the NC dimension makes their light absorption characteristics approach to bulk Si, which means, smaller absorption cross sections. Although large grains have higher electronic density of states, their oscillator strength is smaller 9,10 and consequently, the radiative recombination rate is lower.…”

“…The discussions are basically centered on whether light emission occurs via quantum confinement or via interface states located at the nanocrystals surface. [4][5][6][7][8] It is known that several parameters can contribute to the Si NC PL properties, such as the number and size of crystallites, their surrounding and/or competitive nonradiative processes. For instance, it is well known that passivation of nonradiative interface states enhances the photoluminescence properties of the Si NC without changing the crystallite size.…”