Dielectric function of ZnTe nanocrystals by spectroscopic ellipsometry

Abstract

We have studied the optical properties of ZnTe nanocrystals (ZnTe-nc)by spectroscopic ellipsometry. The ZnTe-nc are embedded in aSiO2 matrix by an ion implantation technique. Two doses of1 × 1016 and5 × 1015 cm−2 of tellurium and zinc ions are implanted in a 250 nm thickSiO2 layer thermally grown on silicon with respective implantationenergies of 180 and 115 keV. Subsequent thermal treatments at800 °C lead to the formation of ZnTe-nc. Their sizes are characterized bytransmission electron microscopy. The ZnTe-nc obtained with the1 × 1016 cm−2 dose are self-organized into two layers parallel to the surface. Their meanradius ranges between 4–17 nm and 7–17 nm. The ZnTe-nc obtained with the5 × 1015 cm−2 dose are self-organized into one layer with a mean radius between 4–17 nm. A critical points(CPs) dispersion model is used to extract the optical responses of the ZnTe-nc. The opticalproperties such as the dielectric function and the second derivative of the dielectricfunction are presented and analyzed. The dielectric function spectra reveal distinctstructures attributed to band gap and optical transitions at higher energy. Thecorrelation between the optical responses and the size of the nanocrystals is also given.