Petrus R. Structural-morphological and optoelectronic properties of thin films of cadmium chalcogenides.

In the dissertation the general principles and features of influence of deposition methods and modifications on structural, morphological and optoelectronic properties of cadmium chalcogenides films for efficiency increase of instrumental structures based on them are established. Technological modes of deposition of semiconductor films with the use of various methods (deposition of films in a quasi-closed volume, high-frequency magnetron sputtering and chemical-surface layer deposition) are substantiated.The choice of the close spaced sublimation method and technological parameters of the deposition process was made based on the thermodynamic analysis of the vapor phase and mass transfer and provides the deposition process in conditions close to equilibrium. The high structural perfection of the films was confirmed by X-ray structural and Raman studies. Scientific analysis of surface morphology, structural and optical properties of CdS, CdSe and CdTe films depending on the deposition method and annealing conditions is carried out. It is established that physical vacuum methods of deposition provide more perfect films by the method of chemical-surface deposition. Based on the structural characteristics, the calculations of the electronic energy structure were performed, and it was found that for cadmium chalcogenides the dispersion of energy levels decreases during the transition from a single crystal massive sample to a thin film. From the density of the states of the electronic energy spectrum for single crystals and thin films of CdS, CdSe, CdTe, it was established that the top of the valence bands is formed mainly by p-states of chalcogen (S, Se, Te) and the bottom of the conduction band by s- and p-states Cd. The nature of the states distribution of the zones that form the band gap indicates the formation of the fundamental absorption edge by the direct zone transitions in the cadmium – chalcogenide sublattice. The dissertation investigates the main optical characteristics as a function of wavelength obtained experimentally (bypass method) and calculated theoretically from the electronic energy spectrum using the Kramers – Kronig ratio. An increase of the band gap of CdS thin films with a decrease in their thickness (d <100 nm) was found, which may be caused by the quantum-size effect.