Budnik A. Size effects in thin films based on Bi2Te3.semiconducting compound

The thesis is devoted to a study of the structure and kinetic phenomena in thin Bi2Te3 films as functions of the film thickness d, with a view to detecting quantum size effects (QSE) and revealing the specificity of their manifestation in 3D-topological insulators (TI), to which Bi2Te3 belongs. The optimal compositions of initial crystals and technological parameters for the preparation of p- and n-Bi2Te3 films with a high structural quality and pre-determined conductivity type by thermal evaporation in vacuum onto glass substrates were identified. The prepared films had a high degree of structural perfection and preferential orientation of crystallites, which determined the possibility of studying QSE in those films. It was established that in Bi2Te3 films, the d-dependences of kinetic properties have an undamped oscillatory character with a large amplitude and can be approximated with sinusoidal functions. The existence of d-oscillations was attributed to the quantization of energy spectrum of holes and electrons. Calculations of the oscillation period d using a model of an infinitely deep potential well yielded values of d which were consistent with the experimental ones. It was suggested that the undamped character of oscillations and their substantial amplitude are connected with a change in the conditions on the film boundaries as a result of the existence of a topological layer, which prevents scattering by defects due to time-reversal symmetry - one of the fundamental properties of TI.