Sapelnikova O. Photoluminescence and local electric fields in two-dimensional structures of macroporous silicon with nanocoatings

Thesis for a Candidate of Phys.-Math. degree in specialty 01.04.18 - Рhysics and chemistry of surface. – O.O. Chuiko Institute of Surface Chemistry of the National Academy of Sciences of Ukraine, Kyiv, 2021. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences on a specialty physics and chemistry of surface. The dissertation is devoted to the determination of the influence of local electric fields in two - dimensional structures of macroporous silicon with CdS nanocrystals on the reduction of nonradiative recombination in light - emitting elements bazed on the system «macroporous silicon - nanocoating». The oscillations of IR absorption determine the intensity of local electric fields in oxidized structures of macroporous silicon with SiO2 layers with a thickness of 5 - 800 nm, which reaches values (8 10)·105 V/cm due to the attenuation of electrical energy in the oxide during the formation of quasi-directional waveguide modes silicon matrix. Light-emitting structures based on oxidized macroporous silicon with a SiO2 nanocoating thickness of 5  30 nm and a layer of ZnO and CdS nanoparticles with a thickness of 8  25 nm were fabricated. The maximum photoluminescence intensity was obtained under the following conditions: (1) the maximum strength of electric field at the Si - SiO2 boundary for both previously crude and purified structures of macroporous silicon with CdS nanocoating; (2) increasing the flow of electrons from the silicon matrix towards the CdS nanocrystals; (3) an increase in the residence time of electrons at the Si - SiO2 interface, which significantly reduces the rate of nonradiative recombination at the CdS – SiO2 interface. It was also found that the maximum strength of electric field at the «silicon – nanocoating» interface corresponds to the maximum photoluminescence intensity. The quantum yield of photoluminescence of CdS nanoparticles on the surface of oxidized macroporous silicon with the optimal thickness of the SiO2 layer increases 3 – 4 times during the first 2 weeks due to evaporation of water molecules from the nanoparticle layer in the polymer and reaches 28%. During further storage of the samples, the spectrum and quantum yield of photoluminescence are almost unchanged. The technology of manufacturing light-emitting nanocrystals on the surface of oxidized macroporous silicon allows to increase simultaneously the quantum yield of photoluminescence, the strength of structures and to protect the surface from degradation. Keywords: macroporous silicon, Si - SiO2 boundary, CdS nanocrystals, Wanier-Stark electrooptical effect, photoluminescence, photoconductivity, electro-optical reflection.