Sarikov A. Structural and phase transformations during formation of Si and 3C-SiC based films and nanocomposites

The thesis is devoted to the elucidation of the mechanisms of external influences on the structure and phase composition of silicon and cubic silicon carbide (3C-SiC) based films and nanocomposites during their formation. A kinetic model of the aluminum induced layer exchange process for growing polycrystalline Si films on foreign non-orienting substrates is proposed. The physical mechanisms of this process as well as their dependence on the characteristics of initial structures and annealing temperature are revealed. Moreover, the metal-induced crystallization mechanism, underlying the layer exchange process, is proved essential to account for the peculiarities of the metal catalyzed growth of Si wire-like crystals in the vapor-liquid-solid and related processes. A thermodynamic theory of the phase separation of SiOx (x < 2) films during high-temperature annealing is proposed. An expression for the free energy of Si oxide as a function of its composition and temperature is derived. The dependence of the phase and structural characteristics of phase separated Si/SiOx nanocomposites on the initial Si oxide stoichiometry and annealing temperature is theoretically grounded. The complete or partial layer intermixing in SiOx/SiO2 superlattices with nanometer thick layers and it dependence on the characteristics of initial superlattices and annealing temperature are theoretically proved. Using molecular dynamics simulations, the evolution of extended defects in 3C-SiC films during growth on Si substrates is simulated. It is demonstrated that the formation of stable Shockley partial dislocation complexes as well as the annihilation of stacking faults in 3C-SiC films are determined by the stress evolution at different stages of the standard two-stage film growth technology. Moreover, the experimentally observed partial dislocations with visible <132> and <143> line directions are found to consist of the stable <011> and <121> line segments. A mechanism of the formation of such dislocation line directions is proposed based on the tendency of energy minimization by reducing dislocation length on the one hand and formation of the lowest-energy segments on the other hand. The structure of the typical extended defect in hexagonal GaP/Si wire-like crystals is revealed. Moreover, the existence of a critical radius of about 7 nm for transition of the stability of Si wire-like crystal structure from the hexagonal to the cubic one is established. The existence of critical radius is due to the larger surface and lower bulk energy of Si in the cubic phase as compared to the hexagonal one