StatusThe thesis was presented on the 21 September, 2021 at the meeting of the Scientific Council and now it is under consideration of the National Council.
Abstract– 1.61 Mb / in romanian
7.47 Mb /
Of the doctoral thesis "Optical and photoelectric properties of gallium sulfide/ gallium selenide nanocomposites - its own oxide" presented by Sprincean Veaceslav, to get a PhD degree in Physics in specialty 134: 01-Physics and technology of materials, Chisinau 2021.
The thesis consists: introduction, four chapters, general conclusions and recommendations, bibliography of 261 titles, 132 pages of basic text, 92 figures, 20 tables, 49 formulas. The results are published in 18 scientific papers.
Research area: new functional nanotechnology and nanomaterials.
Purpose of the work and tasks of the study: This work is aimed at developing technological processes for the preparation of nanostructured materials and composite structures with appropriate optical and photoluminescent properties based on semiconductors with DSO of the A2IIIB3VI group and lamellar semiconductors of gallium monosulfide and gallium monoselenide undoped and doped/intercalated with Zn and Eu and considering the prospects for their use in opto-and photovoltaic devices for ultraviolet and visible range. Synthesis of nanostructured compound β-Ga2O3, compounds (β-Ga2O3)-lamellar semiconductor (GaS, GaSe) and β-Ga2O3-semiconductor with intrinsic structural defects Ga2S3 and Ga2Se3 not intercalated and intercalated with Zn, Ga, and study of their photoelectric and optical properties. Determination of the mechanisms of generation and recombination of nonequilibrium charge carriers in oxide semiconductors, in composites and structures with nanostructured semiconductors based on gallium sulfide/selenide, not intercalated and intercalated with Ga and Zn. Evaluation of the role of intercalations of Zn, Ga, and Eu3+ ions in the formation of emission luminescence spectra of micro-and nanostructured β-Ga2O3 compounds and β-Ga2O3 structures on the GaS, GaSe, Ga2S3, and Ga2Se3 substrate, not intercalated and intercalated with Ga and Zn.
Scientific novelty and originality: The technologies for obtaining the micro- and nanocrystalline composites from semiconductor materials of the A2IIIB3IV (Ga2S3 and Ga2Se3) group micro-and nanostructured from sulfide and selenide of zinс, by the method of thermal treatment (TT) in Zn vapors of single crystals of GaS, GaSe, Ga2S3, and Ga2Se3, were developed. It was shown that the controlled TT process in Zn vapors produces semiconductor composite layers ZnS/Ga2S3 , ZnSe/Ga2Se3, GaS/ZnS, and ZnSe/GaSe, from which micro-and nanocomposites β-Ga2O3 and ZnO are obtained by TT in air. The correlation between the type of β-Ga2O3 nanoformations and the crystal structure of a semiconductor subjected to thermal treatment in air was established. It was shown that, upon TT in air, single crystals of GaSe doped with Eu, formed a composite material of nanoformations β-Ga2O3:Eu3 with fluorescence in the green-red spectral region.
The solved scientific problem: Using TT in Zn vapor of GaS, GaSe, Ga2S3 single crystals, and Ga2Se3 polycrystals, the composites of micro-and nanocrystallites of these materials with ZnS and ZnSe, the nanoformation of β-Ga2O3 and ZnO composites, with improved physical properties and expansion of the range of functional applications of these materials in optoelectronic devices, were obtained.
The theoretical significance and practical value of the work: It was found that Zn and O2 intercalated into gallium sulfides and selenides, at high temperatures, forms chemical bonds that serve as germs for the crystallization of ZnS compounds from ZnSe. The type of β-Ga2O3 nanoformations (nanowires, lamellas, granules, or blocks), formed by TT at high temperatures on the surface gallium sulfide and selenide, depends on the crystal structure and the ability to absorb gas on the surface of these materials; therefore, nanowires/nanolamels prevail on the surface of GaS/GaSe crystals, while the β-Ga2O3 layer on the surface of DSO crystals dominates in the form of granular formations. Based on the micro-and nanocomposites β-Ga2O3, β-Ga2O3-ZnO, and β-Ga2O3:Eu3+, it is possible to develop sources of selective radiation in a wide wavelength range from UV to near-IR. The mechanism of generation-recombination of nonequilibrium charge carriers in micro-and nano-formations of β-Ga2O3 and ZnO has been established. The possibility of using the β-Ga2O3 and β-Ga2O3-GaS structures as photoreceptors for the UV and blue-UV regions of the spectrum was demonstrated.
Implementation of scientific results: The micro-structured thin layers β-Ga2O3:Eu3+ and the planar structures β-Ga2O3-ZnO being photoluminescent materials at excitation with UV radiation as a whole with solar cells based on Si widen the spectral range of photosensitivity and respectively the light-electricity conversion efficiency.
Photoresistors based on β-Ga2O3 layers on gallium sulfide/selenide substrate with sensitivity in the UV-I region (insensitive to the solar radiation at the earth surface) can be used to detect high-temperature sources, electrical discharges in gases, and insulators at high voltage lines.