Orest Kvitsiani

The current state of the share of solar cells in the world energy supply and future growth trends are discussed. Physical foundations of photovoltaic cells and advances in technology to increase conversion efficiency are described. The advantages and disadvantages of individual approaches are evaluated. It is proposed to improve the conversion efficiency of the new generation of solar cells by adding a nanostructured layer based on the III-V semiconductor.

Simple method of preparation of nanocrystals on the III-V semiconductor surface is described. This method includes electrochemical deposition of group III metals on electrochemically etched semiconductor surface. The chlorides of metals are used for Indium and Gallium deposition. After layer metallization wafers are annealed in hydrogen at the various temperatures in order to form nanocrystals on the surface. Influence of annealing temperature on the characteristics of structures is investigated and possible mechanism of interactions between metal and semiconductor during formation of nanocrystals are discussed. Application of obtained structures for the Multiple Junction Solar Cells is proposed.

Solar cells (SCs) based on III-V semiconductors are reviewed. Presented work emphases on the Solar Cells containing Quantum Dots (QDs) for next-generation photovoltaics. In this work the method of fabrication of InP QDs on III-V semiconductors is investigated. The original method of electrochemical deposition of metals: indium (In), gallium (Ga) and of alloys (InGa) on the surface of gallium phosphide (GaP), and mechanism of formation of InP QDs on GaP surface is presented. The possibilities of application of InP/GaP/Si structure as SC are discussed, and the challenges arising is also considered.

Nanotechnology is defined as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers. Although modern semiconductors manufactured are measured in nanometers, production of semiconductors is not traditionally classed as nanotechnology. Nanotechnology is likely to manifest itself in the semiconductor industry as semiconductor devices. The examples of modern semiconductor technology are quantum dots, quantum wires or nanotubes and quantum wells. The physical properties and various methods of fabrication III – V semiconductor QD’s are described in [1]. Because of its dimensions nanostructured materials are useful to interact with light, and it is thought that twenty-one century will be the era of photons. Although one use of III – V semiconductor QD’s is high effective light emitted devices, as well as and wavelength conversion changing emitted light to the desired spectrum, the resent works show that two main field of application QD are: a new class of fluorescent materials for biosensor, and energetic materials for new generation solar cells [2].

The method of electrochemical deposition of metals (In, Ga, Al, Sb, Bi, Cu, Ni, Ag, Pt, Pd, Fe) on semiconductor surface was used for fabrication of various semiconductor devices [2 – 5]. By deposition of the III group metals (In, Ga) on III – V semiconductor GaP, followed with heat treatment in hydrogen, it was obtained the nanostructured layer InxGa1–xP on GaP surface, and the possibility of application of obtained structures for quantum dot solar cell was theoretically investigated [2].

The current research is an attempt of obtaining spintronic material by original method of electrochemical deposition of ferromagnetic metals on the GaAs surface [4] and investigation of their electrical and photoelectric properties. The process steps are improved and novel process techniques are developed for manufacturing of GaAs-based devices.

A brief overview of ongoing work to increase the efficiency of solar energy converters and reduce the cost of energy produced shows the importance of Group III-V semiconductors in creating a new generation of quantum dot solar cells. The physical basis of the operation of intermediate-band solar cells is described. Based on a study of the photoelectric properties of photosensitive structures based on III-V semiconductors, namely broadband semiconductor gallium phosphide (GaP) and structures obtained by increasing InGaP and / or InP nanocrystals on its surface, the possible use of gallium phosphide in the intermediate generation is shown.

The conference / seminar was held on February 24-25, 2011 with the financial support of Shota Rustaveli National Science Foundation, grant (# GNSF / ST08 / 4-426); Scientific papers of the Vladimer Chavchanidze Institute of Cybernetics of the Georgian Technical University were presented at the event. The submitted works were published by the publishing house "Technical University" in the collection "Photonics".

We present the results of experimental studies of physical properties of the detection process of GaAs Schottky diodes for terahertz frequency radiation. The development of technology in the THz frequency band has a rapid progress recently. Considered as an extension of the microwave and millimeter wave bands, the THz frequency offers greater communication bandwidth than is available at microwave frequencies. The Schottky barrier contact has an important role in the operation of many GaAs devices. GaAs Schottky diodes have been the primary nonlinear device used in millimeter and sub millimeter wave detectors and receivers. GaAs Schottky diodes are especially interesting due to their high mobility transport characteristics, which allows for a large reduction of the resistance-capacitance (RC) time constant and thermal noise.

In This work are investigated the electrical and photoelectric properties of GaAs Schottky diodes. Samples were obtained by deposition of different metals (Au, Ni, Pt, Pd, Fe, In, Ga, Al) on semiconductor. For fabrication metal-semiconductor (MS) structures is used original method of metal electrodepositing. In this method electrochemical etching of semiconductor surface occurs just before deposition of metal from the solution, which contains etching material and metal ions together. For that, semiconductor surface cleaning processes and metal deposition carries out in the same technological process. In the experiments as the electrolyte was used aqueous solution of chlorides. Metal deposition was carried out at room temperature.

Quantum dots are man-made artificial atoms. The term Quantum Dots was coined by Mark Reed and is used in the plural. Quantum dots are semiconductor structures 1-100 nanometers in size whose excitons are limited to all three spatial dimensions. Such structures have properties that occupy an intermediate state between the properties of volumetric semiconductors and the properties of a discrete molecule, allowing the action of quantum mechanical events to be studied at distances approximately 100 times the size of real atoms.

Thin ferromagnetic films (Fe, Ni) on GaAs substrates have involved as a model system for the integration of magnetic materials with semiconductors. For practical applications, it is highly desirable that the injection of spin currents should be electrical and the injecting from a classical ferromagnetic metal in a metal/semiconductor heterostructure is most direct way for spin injection. In majority of investigations metallic thin films has been deposited at elevated temperatures, however, due to the diffusion of Ga and As into the film even at room temperature no sharp interface, satisfying requirements of spintronic devices, is formed. In order to reduce intermixing effects, Fe was recently deposited also at room temperature, and good epitaxial growth was reported without formation of a dead magnetic layer. Here we report the physical properties of structure obtained via electrochemical deposition metallic (Fe, Ni, Pd) thin films on GaAs substrate. Electrochemical deposition is a low-energy process and offers inexpensive alternative for potentially fabricating abrupt Ferromagnetic Metal/GaAs interfaces. Thin ferromagnetic films on GaAs substrates were obtained by electrochemically deposition of ferromagnetic metal on the previously electrochemically etched surface of semiconductor. The aqueous solution of chloride was used for deposition of metals. There were studied current-voltage and capacitance-voltage characteristics for determination interfaces quality, and the results of investigation physical properties of interface are presented in this paper.

The results of the experimental study of the voltamper and photo-spectral characteristics of S-type voltammetric structures with negative impedance obtained on high-partially compensated gallium phosphide (ρ = 108 ohms) are presented. The war contacts were made by indium melt in a hydrogen atmosphere at 600 ° C. The diodes glowed green at room temperature. The study of the spectral characteristics of the samples showed a strong dependence of the spectral distribution of the photoconduction on the electric field. Based on the study of the voltammeter characteristic, it is shown experimentally for the first time that the anterior section of the negative differential resistance of the voltammeter characteristic consists of three quadrants and the area of ​​rapid (almost vertical) increase of current, which may be caused by the presence of In the study of injected currents in compensated semiconductors and dielectrics discussed by Lampert. Lampert's theoretical model is used to explain the mechanism for the generation of a negative differential resistance on a voltammeter characteristic.

Doctoral Thesis Referee

Master Theses Supervisor

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Scientific editor of monographs in foreign languages

Scientific editor of a monograph in Georgian

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Member of the editorial board of a peer-reviewed scientific or professional journal / proceedings

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Research articles in high impact factor and local Scientific Journals

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