Design and Optical Characterization of Se/(Al, Ag)/Se Interfaces رسالة ماجستير

Abstract

In this thesis the nanosandwiching technique is employed to alter the structural and optical properties of Selenium (Se). Particularly, two Se layers are sandwiched with Al and Ag metals of thicknesses of 50-100 nm. The resulting sandwiched films are investigated by means of X-ray diffraction and UV- visible spectrophotometry and found to exhibit different structural properties depending on the type of metal. Particularly, the freshly characterized films of Se sandwiched with Al layer exhibit polycrystalline nature compared to the pure as grown Se film. On the other hand, the Ag doped samples are observed to be of amorphous nature regardless of the thickness of Ag layer. Optically, while the Al nanosandwiching of Se systematically decreases the energy band gap with increasing Al thickness, the Ag metal doesn’t show systematic engineering of the band gap. Furthermore, the dielectric dispersion analysis on the films, has shown that the shape of dielectric spectra completely changes upon metal nanosandwiching. The modeling of the imaginary part of the spectra, in accordance to Drude-Lorentz theory reveales the optical conduction parameters presented by plasmon frequency, free carrier density, drift mobility and scattering time at femto second level. While the Al nanosandwiching of Se systematically decreases the drift mobility, increases the free carrier density. The Ag nanosandwiching increases the drift mobility and the free carrier density.