F. Ahmed, A. En Naciri, J. J. Grob, M. Stchakovsky, L. Johann

Dielectric function of ZnTe nanocrystals by spectroscopic ellipsometry

Nanotechnology 20 (2009) 305702

We have studied the optical properties of ZnTe nanocrystals (ZnTe-nc) by spectroscopic ellipsometry. The ZnTe-nc are embedded in a SiO₂ matrix by an ion implantation technique. Two doses of 1 x 10¹⁶ and 5 x 10¹⁵ cm^-2 of tellurium and zinc ions are implanted in a 250 nm thick SiO2 layer thermally grown on silicon with respective implantation energies of 180 and 115 keV. Subsequent thermal treatments at 800 °C lead to the formation of ZnTe-nc. Their sizes are characterized by transmission electron microscopy. The ZnTe-nc obtained with the 1 x 10¹⁶ cm^-2 dose are self-organized into two layers parallel to the surface. Their mean radius ranges between 4-17 nm and 7-17 nm. The ZnTe-nc obtained with the 5 x 10(15) 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 optical properties such as the dielectric function and the second derivative of the dielectric function are presented and analyzed. The dielectric function spectra reveal distinct structures attributed to band gap and optical transitions at higher energy. The correlation between the optical responses and the size of the nanocrystals is also given.

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