Abstract
One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity. In this study we explore the limits of external quantum yield of photoluminescence of solid-state dispersions of Si nanocrystals in SiO2. By making use of a low-temperature hydrogen passivation treatment we demonstrate a maximum emission quantum efficiency of approximately 35%. This is the highest value ever reported for this type of material. By cross-correlating PL lifetime with EQE values, we obtain a comprehensive understanding of the efficiency limiting processes induced by Pb-defects. We establish that the observed record efficiency corresponds to an interface density of Pb-centers of 1.3 × 1012 cm12, which is 2 orders of magnitude higher than for the best Si/SiO2 interface. This result implies that Si nanocrystals with up to 100% emission efficiency are feasible.
Highlights
One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity
As a matter of fact, it is well known that the emission efficiency of Si NCs depends crucially on the surface quality[3] and relatively high emission efficiencies have been reported for colloidal Si NCs with engineered surfaces[4]
Since the passivation treatment is performed at temperatures below those necessary to alter the Si aggregation process[12], this effect cannot originate from an actual change of the NC size
Summary
One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity. We investigate the natural emissivity efficiency limit of the basic, and so far only truly up-scalable form of Si NC networks: thin-film solid-state dispersions of Si NCs embedded in SiO2 In this way we establish the true application potential of this material. By cross-correlating PL lifetime with EQE, we conclude that energy transfer towards “defected” NCs containing a Pb-center strongly reduces the internal quantum efficiencies In this investigation, we make use of Si NCs in SiO2, prepared by sputtering and a high-temperature heat treatment (at 1100, 1150 and 1200 °C) to induce Si precipitation and NC formation – see Experimental Methods for more material details. Similar to previous reports[11], the average size of NCs www.nature.com/scientificreports/
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