Optical properties of embedded ZnTe nanocrystals in SiO₂ thin layer

Abstract

We have studied the optical properties of ZnTe nanocrystals (ZnTe-nc) embedded in a SiO 2 matrix by spectroscopic ellipsometry. The ZnTe-nc are embedded in a SiO 2 matrix by ion implantation technique. The dose of 2.9 Â 10 16 cm À2 of tellurium and zinc ions are implanted in a 250 nm thick SiO 2 layer thermally grown on Si with respective implantation energies of 180 and 115 keV. Subsequent thermal treatments at 700 8C lead to the formation of ZnTe-nc. Their size is characterized by transmission electron microscopy. Variable angle ellipsometric measurements are performed in air at room temperature at angles of incidence of 55, 60, and 658. By taking into account defects caused by ion implantation in silica matrix, the critical points (CPs) dispersion model is used in order to extract the optical responses of the ZnTe-nc. The determined dielectric function spectra reveals distinct structures attributed to direct band gap and optical transition at higher energy. The observed structures are analyzed by fitting second derivative spectrum of the imaginary part of dielectric function with analytic CP line shapes. Results show good agreement with CPs data.

Near infrared to ultraviolet optical properties of bulk single crystal and nanocrystal thin film iron pyrite

“…As can be seen in table 3, a blue shift occurs in the two lowest energy detectable critical points of the bulk crystal fraction of FeS 2 in the nanocrystalline film as compared with the critical point energies seen in the bulk sample only. For films comprised of small nanocrystallites, such as those seen in figure 1, this kind of effect is significant [35]. Because of the high surface-to-volume ratio in the nanocrystal film, surface defects, such as vacancies and dangling bonds, are commonly observed in addition to defects already present within the bulk of each crystallite [36].…”