Nitrogen at the Si-nanocrystal / SiO2 interface and its influence on luminescence and interface defects


Nitrogen at the Si-nanocrystal / SiO2 interface and its influence on luminescence and interface defects

Hiller, D.; Götze, S.; Munnik, F.; Jivanescu, M.; Gerlach, J. W.; Vogt, J.; Pippel, E.; Zakharov, N.; Stesmans, A.; Zacharias, M.

The influence of the high temperature annealing ambient (N2 or Ar) on size controlled Si nanocrystals (NCs) in SiO2 ranging from ~2 to ~6 nm has been investigated in detail. Generally, N2 annealing is beneficial as the dangling bond density (Pb-defects at the NC/SiO2 interface) is about half accompanied by a doubled PL intensity. The N-related PL blueshift was found to be pronounced only for the small NCs whereas it appears to be insignificant for larger NCs. The origin of this N-blueshift was previously attributed to NC growth suppression by the presence of N. 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 ToF-SIMS and ESR: Besides the distinct N-enrichment in the NC-layer, the K0-center (•Si≡N3) was detected indicating the formation of an interfacial N layer at the NC/SiO2 interface. ERD analysis enabled the quantification of the incorporated N as well as the excess Si. Combined with TEM 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 ~ 5×1014 N-atoms cm-2 exist at the NC, which is well in accordance to the optimum value of the bulk Si/SiO2 interface. These results support our recently suggested explanation for the N-blueshift that is based on the influence of the polarity of the surface terminating groups on the bandgap of the NC.

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Publ.-Id: 14077