CdSe based electro-optical systems designed for optoelectronic applications رسالة ماجستير

Abstract

In this thesis we aimed to enhance the optical properties of CdSe thin films by coating it onto a highly conductive SiO2 substrates. Thin films of CdSe are coated by the thermal evaporation techniques onto conductive SiO2 substrates under a vacuum pressure of 10-4 mbar. Stacked layers of SiO2 films comprising Au nanosheets (SAS) are used. It is observed that SiO2 substrates containing Au nanosheets in it structure significantly modulate the structural and optical properties of CdSe. Namely, the lattice constants of hexagonal CdSe decreased upon replacement of glass by SAS substrates. The micro strain, stacking fault percentage and defect density also decreased indicating the enhanced crystalisity of the films by SAS substrates. In addition it is observed that SAS films don’t play a significant role on the energy band gap, but forms energy tails in the band gap. The exponential tail states narrows as the thickness of Au layer increases. On the other hand, the dielectric dispersion analyses have shown that the dielectric constant spectra are determined by three oscillators which blue-shifts upon replacement of glass by SAS substrates. The dielectric constant values decreased with increasing Au layer thickness in the substrate owing to the freer charge density resulting from a thicker Au layer. On the other hand, the optical conductivity spectra which were modeled using Drude-Lorentz approach showed interesting features. Particularly, the optical conductivity of CdSe increased and the free carrier density increased after using SAS substrates. These features make the films under study more adequate for optoelectronic applications.