P b ( ) centers at the Si-nanocrystal/SiO2 interface as the dominant photoluminescence quenching defect

Abstract

The correlation of paramagnetic defects and photoluminescence (PL) of size controlled Si nanocrystals (NCs) has been studied as a function of annealing ambient (Ar or N2) and subsequent H2 treatment. The dominant defects measured by electron spin resonance are interfacial Pb(0) and Pb1 centers. Whereas the latter appears to play only a minor role in PL quenching, a pronounced correlation between Pb(0) density and PL intensity is demonstrated. Annealing in N2 is found to be superior over Ar both in terms of PL performance and defect densities. The origin of the PL blueshift found for N2 annealing compared to Ar was previously interpreted as a growth suppression of the Si clusters due to incorporation of N atoms or a silicon consuming nitridation at the NC/SiO2 interface. The results presented here, demonstrate the blueshift to be more pronounced for small NCs (∼2 nm) than for larger ones (∼4.5 nm). Therefore, we suggest an alternative interpretation that is based on the influence of the polarity of surface terminating groups on the electronic properties of the NCs.