Sergey Levichev

On the basis of a comprehensive study of the structural and electronic properties of InAs/GaAs quantum dots grown by vapor-phase epitaxy at atmospheric pressure, a structural model of the quantum dots as three truncated pyramids adjoined at their bases is chosen. The model takes into account the diffusive smearing of the composition near the base and lateral surface as well as the segregation of indium near the vertex. It is established that the wave functions of charge carriers in the ground state are localized in a comparatively small region of the quantum dot near its vertex.

The temperature-dependent photosensitivity of InAs/GaAs self-assembled quantum dots at different vertical electric field strengths was studied. The analysis was performed with the help of a theoretical model of the carrier escape process, taking into account the deformation potential and the diffusion broadening of the heterointerface between the InAs quantum dots and the GaAs substrate, as well as excitonic effects. Conducted research allowed to determine the temperature dependence of carriers lifetimes in QDs relatively to the different emission mechanisms at several magnitudes of electric field strengths.

Photoelectric spectra of heterostructures containing InAs quantum dots (QDs) produced in different technological regimes were studied. A simple nondestructive method to reveal a bimodality of the QDs’ size distribution was described. The method based on the analysis of the shape of InAs/GaAs QDs’ photoelectric spectra and their temperature dependencies. The quantitative analysis of the temperature dependencies of the photoelectrical spectra was performed. All possible emission processes occurring from quantum confined levels to the semiconductor matrix were considered at the simulation. The surface concentration of the QDs was estimated.

In this work, SiGe/SiO₂ multi-layer (ML) films with layer thickness in the range of a few nanometers were successfully fabricated by conventional RF-magnetron sputtering at 350 °C. The influence of the annealing treatment on SiGe nanocrystals (NCs) formation and crystalline properties were investigated by Raman spectroscopy and grazing incidence x-ray diffraction. At the annealing temperature of 800 °C, where well defined SiGe NCs were observed, a thorough structural investigation of the whole ML structure has been undertaken by Rutherford backscattering spectroscopy, grazing incidence small angle x-ray scattering, high resolution transmission electron microscopy, and annular dark field scanning transmission electron microscopy. Our results show that the onset of local modifications to the ML composition takes place at this temperature for annealing times of the order of a few tens of minutes with the formation of defective regions in the upper portion of the ML structure. Only the very first layers over the Si substrate appear immune to this problem. This finding has been exploited for the fabrication of a defect free metal-oxide-semiconductor structure with a well-defined single layer of SiGe NCs. A memory effect attributed to the presence of the SiGe NCs has been demonstrated by high frequency capacitance-voltage measurements.