Nitrogen at theSi-nanocrystal/SiO2interface and its influence on luminescence and interface defects

Abstract

The influence of the high-temperature annealing ambient, i.e., ${\text{N}}_{2}$ and Ar on size controlled Si nanocrystals (NCs) ranging from $\ensuremath{\sim}2$ to $\ensuremath{\sim}6\text{ }\text{nm}$ 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 $(^{\ifmmode\bullet\else\textbullet\fi{}}\text{S}\text{i}\ensuremath{\equiv}{\text{N}}_{3})$ 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 $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{N}\text{ }\text{atoms}\text{ }{\text{cm}}^{\ensuremath{-}2}$ 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.