The influence of the high-temperature annealing ambient, i.e., ${\text{N}}_2$ and Ar on size controlled Si nanocrystals (NCs) ranging from $\sim 2$ to $\sim 6\text{nm}$ embedded in ${\text{SiO}}_2$ has been investigated in detail. Generally, ${\text{N}}_2$ annealing is proven to be beneficial as the dangling bond density (${\text{P}}_{\text{b}}$ defects at the $\text{NC}/{\text{SiO}}_2$ interface) is about half, accompanied by a doubled photoluminescence (PL) intensity. The PL blueshift of ${\text{N}}_2$ annealed samples compared to Ar-annealed samples (N-blueshift) was found to be pronounced only for small NCs whereas it appears to be insignificant for larger NCs. The origin of this N-blueshift was previously attributed to a growth suppression of the NCs by the presence of N during the annealing process. However, no evidence for this assumption is found by time-resolved PL, as the luminescence decay times are similar despite considerable N-blueshift. The exact location of the N incorporated during annealing was investigated by time-of-flight-SIMS and electron-spin resonance. Besides the distinct N enrichment in the NC layer, the ${\text{K}}^0$ center $\left({}^{•}\text{S}\text{i}\equiv {\text{N}}_3\right)$ was detected indicating the formation of an interfacial N layer at the $\text{NC}/{\text{SiO}}_2$ interface. Elastic recoil detection analysis enabled the quantification of the incorporated N as well as the excess Si. Combined with transmission electron microscopy analysis (determination of NC size) the calculation of the NC density per superlattice layer and the thickness of the interfacial N layer were achieved. It turns out that $\sim 5\times {10}^{14}\text{N}\text{atoms}{\text{cm}}^{-2}$ exist at the NC surface, which is well in accordance to the optimum value of the bulk $\text{Si}/{\text{SiO}}_2$ interface. These results strongly support our recently suggested explanation for the N-blueshift that is based on an increased NC band gap by the influence of interfacial N on the polarity of the surface terminating groups.

• Received 27 May 2010

DOI:https://doi.org/10.1103/PhysRevB.82.195401