Growth and characterization of iron selenide thin films containing aluminum nanosheets رسالة ماجستير

Abstract

In this thesis, iron selenide thin films of thickness of 0.5 um are prepared by the thermal evaporation technique. Films which are coated onto glass substrate, under vacuum pressure of 5mbar are sandwiched with Al nanosheets of thickness of 50 nm. The thesis focus on comparing the structural, optical and electrical properties of the films before and after insertion of Al nanosheets. Remarkable induced crystallization process is observed in the iron selenide films as a result of Al participation. In addition, the sandwiching of the iron selenide thin films with Al nanosheets, resulted in enhanced optical absorbability in the visible and infrared ranges of light. It also red shifts the energy band gaps from the visible range to the infrared range of light. The shrinkage in the energy band gap is accompanied with remarkable increase in the electrical conductivity at room temperature. Temperature dependent investigations of electrical conductivity in the temperature range of 100-350 K have shown that the conductivity is dominated by the thermal excitation of charge carrier in the high temperature range and by the variable range of hopping conduction at low temperatures. Insertion of Al nanosheets, highly shifted the conductivity activation energy forcing the iron selenide samples to display degenerate semiconductor characteristics. Furthermore, the analysis of the dielectric spectra in the visible range and infrared ranges of light have shown that the 50 nm thick Al nanosheets are sufficient to improve performance of iron selenide. The dielectric constant increased nonlinearly with decreasing incident light energy, making the films more appropriate for passive and dynamic mode device fabricators.