Mazur T. Defective subsystem, optical and electrical properties of impurity-free and doped cadmium telluride films.

Based on experimental studies and relevant theoretical calculations, the analysis of the influence of cadmium telluride thin film vapor technology on the formation of a system of defects, which determines the complex of their structural, electrical and optical properties for practical use as materials for optoelectronics and photoelectric energy conversion. In the second section of the dissertation, the general principles of the methods used in the work of synthesis of binary CdTe (isothermal annealing, two-temperature annealing), control of deviation from stoichiometry and deposition from the vapor phase are given: the "hot wall" method and the method of open evaporation in vacuum. The technological features of the used installations are specified. The method of forming nanostructured surface layers by doping from aqueous solutions and the preparation of p-CdTe layers is described detail. Technological factors that affect the structural, electrical and optical properties of such layers are identified. The list of used methods of film quality control (chemical and phase compositions, morphology of the surface and microhardness of thin films based on CdTe) and the description of the corresponding equipment are given: atomic force and electron scanning microscopy, profilometer, interferometer. As for optical and spectral research methods, a description is given of the spectral setup used in this work to study optical absorption, optical reflection, an optical radiation modulator, a setup for studying λ-modulated optical spectra, a setup for measuring photoluminescence spectra, a diffraction monochromator and a photomultiplier. The features of measuring the electrical parameters of CdTe thin films are shown on the functional block diagram of the installation for automated measurements of the photoelectric parameters of impedance semiconductor films, as well as a list of software used for processing the obtained experimental data. In the third section, the analysis of the crystal structure of crystals and films of CdTe and the quasi-chemical equations of nonstoichiometric cadmium telluride films are proposed. Based on the use of quasi-chemical equations, the dependence of the equilibrium concentration of superior intrinsic atomic defects on the partial pressure of cadmium vapor and the annealing temperature is determined. The analysis of the behavior of dominant intrinsic point defects in cadmium telluride films and their experimental confirmation by photoluminescence methods is performed. A series of test measurements of impedance samples was carried out. The photosensitivity of CdTe films, which is an effective parameter in determining the photoconductivity, has been investigated. The application of thin-film CdTe heterostructures in solar energy is also considered. The electrical properties of the layers formed by doping the surface of the CdTe crystal with Ca and Li impurities are investigated. It was found that the calculated diffusion coefficient for Li ions turned out to be more than three times higher than for Ca ions, since the ionic radius of Li is much smaller (76 pm versus 99 pm for Ca). The calculated specific electrical conductivity of the n-type surface layer at the same dopant concentrations and exposure times turned out to be more than an order of magnitude higher. This made it possible to reduce the total resistance by a factor of 10-20 when going from doping with Ca to doping with Li.