Kupchak I. Electronic characteristics of quantum-size structures in the dielectric matrix

The thesis contains results of exciton spectra calculations for semiconductor quantum gaps, wires and dots embedded in the dielectric matrix. Calculations have been made using effective mass and quadratic dispersion low approximations. The exciton binding energies, the energies of main exciton transition and the characteristic times of direct radiative exciton recombination (or pseudo-direct radiative recombination in the case of indirect-gap semiconductors like Si) have been obtained as functions of the structure thickness. Both finite band off -sets for electrons and holes at heterointerfsces and penetration of electric field lines of electron-hole interaction into the dielectric matrix have been taken into account for the first time. It was shown that polarization of heterointerface and adjacent regions in such quantum-size structures can lead to a substantial increase of Coulomb electron-hole interaction energy and, correspondingly, to large shift of the total energy of exciton transition. The characteristic times of radiative exciton recombination in indirect-gap semiconductor quantum-size structures have been shown can be non-monotonous (oscillating) functions of the characteristic size. Within the framework of proposed model the spectra of steady and time-resolved photoluminescence (PL) in silicon quantum-size structures have been calculated and compared with experimental PL spectra. The kinetics of the exciton PL has been investigated in details. It was shown that the main reason of exciton PL band broadening in such structures is the effect of quantum-mesoscopic fluctuations due to small number of constituting atoms at least in one of the direction (direction of size quantization), when even one atomic-scale defect in the nanocrystal, adjacent layer of dielectric matrix or dangling bond at the heterointerface substantially shifts the energy of exciton transition in the ensemble of nanocrystals with equal characteristic sizes.