P_b(0) centers at the Si-nanocrystal/SiO₂ interface as the dominant photoluminescence quenching defect

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 P_b(0) and P_b1 centers. Whereas the latter appears to play only a minor role in PL quenching, a pronounced correlation between P_b(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.