Doctoral Theses

“Electronics and photonics”

  • Theme: Memristor matrices for post-digital electronics
    Supervisor: Ing. B. Hudec, PhD.Department of III-V Semiconductors )
    Abstract: Memristors are elementary electronic components with the structure of a capacitor, where their resistance can be altered by an applied voltage, and they remember this change. The resistance of so-called analogue memristors is continuously tuneable in several orders of magnitude range, not just by DC but also with AC pulses of both polarities. This makes memristors a hot iron in the post-digital electronics domain, where they can be effectively utilised in a fuzzy logic or as synapses of hardware neural networks in neuromorphic chips, where the resistance modulation can be directly mapped to the synaptic weight change.
    The subject of the thesis will be the research and development of analogue memristors where the active layers are ultra-thin (~nm) oxides will be grown by atomic layer deposition (ALD), and their subsequent electrical characterisation. Various spectroscopic techniques of material analysis will be used among with the physics of electron transport in dielectrics for a broader understanding of the working principles and design of these devices. Memristors will be integrated into matrix structures (memristor crossbar array) which will be coupled with control electronics (ADC/DAC, FPGA) to demonstrate their utilisation in neuromorphic chips or in fuzzy logic.
    The thesis will be a part of a wider project focused on memristor chip development. The student will be part of a research team where he or she will not only grasp a detailed understanding of used characterisation and analytic techniques but also learn the whole process of the development and application of electronic devices.
  • Theme: Technology of epitaxial growth of (ultra)wide bandgap semiconductors using metalorganic chemical vapour deposition (MOCVD) and investigation of their structural, electrical, and optical material properties
    Supervisor: Ing. F. Gucmann, PhD. ( Department of III-V Semiconductors )
    Co-advisors: RNDr. Kristína Hušeková (Oddelenie fyziky a technológie nanoštruktúr)
    Abstract: Semiconductor materials with bandgap energies (Eg) exceeding that of Si or GaN (Eg ~ 1.1 eV or 3.4 eV), i.e. (ultra)wide bandgap (UWB) materials offer great potential for manufacture of future electronic devices with increased radiation hardness, efficiency, and reliability, and capability of operation at high voltages. UWB-based electronic devices bring the opportunity in rapid deployment of modern, environmentally friendly technologies such as electric transportation (e.g. electric cars, trains, ships, planes) or more efficient electric energy transformation and handling in end-user consumer electronics with strong implications for decreasing of the CO2 levels production.
    Gallium oxide (Ga2O3) represents a modern semiconductor material candidate for future high-voltage (>8 kV) and/or high-power electronic devices owing to its unprecedented material properties such as ultrawide bandgap energy (Eg ~ 4.8-5.4 eV), high theoretical breakdown field (Ebr ~ 8 MV/cm), and relatively simple synthesis of thin films and bulk crystals.
    The main focus of this thesis will be a systematic study of epitaxial growth of thin film Ga2O3 or similar materials, e.g. (AlxGa1-x)2O3 or (InxGa1-x)2O3 of various crystal phases and on various substrates (e.g. Al2O3, SiC) using modified metalorganic chemical vapour deposition (MOCVD) techniques and investigation of the material properties of prepared layers (structural, electrical, and optical). Early stages of Ga2O3 growth will be studied in detail to understand the chemical and physical processes participating in the epitaxial growth.
    For this study, we will use the state-of-the-art technological equipment and methods, available at the Institute of Electrical Engineering, SAS and Institute of Physics, SAS. A successful candidate will acquire a hands-on experience with the wide range of experimental techniques for material diagnostics (e.g. X-ray diffraction, atomic force microscopy, Raman spectroscopy, and various advanced electrical methods).
  • Theme: Transistors based on semiconducting 2D materials
    Supervisor: Ing. Milan Ťapajna, PhD.Department of III-V Semiconductors )
    Co-advisor: RNDr. Dagmar Gregušová, DrSc.
    Abstract: The discovery of graphene has triggered unprecedented research in 2-dimensional (2D) materials, which can form one-atom-thick sheets with extraordinary properties. A semiconducting nature of some 2D materials enables their use as channel material in the field-effect transistors. Such devices are expected to exhibit not only improved performance in terms of switching speed and low power consumption, but also to allow further reduction in device dimensions, essential for the fabrication of next-generation integrated circuits. In addition, 2D materials represent a promising candidate for a variety of optoelectronic, energy storage, and sensing devices.
    One of the most promising classes of 2D materials are transition metal dichalcogenides (TMDs) and post-transition metal chalcogenides (PTMCs). These materials show anisotropic electrical and optical properties that are also depend on number of atomic layers. The PhD work aims the development of metal-oxide-semiconductor field-effect transistors (MOSFETs) with channel based on 2D materials and study their transport properties. We will focus on large-area few-layer films (such as PtSe2, GaSe,…) grown by sulfurization and selenization. The MOSFET technology using both, top-gate as well as bottom-gate approach will be developed. Besides electrical properties, optical properties of the prepared 2D materials will be also investigated.
  • Theme: The radiation hardness study of ionizing detectors based on SiC and diamond
    Supervisor: Mgr. Bohumír Zaťko, PhD. (Department of Microelectronics and Sensors )
    Abstract: The aim of the thesis is the technology preparation of ionizing detectors, study of electrical and detection properties and the influence of radiation dose on its performance. Used detection materials are high-quality epi-layer of 4H-SiC, polycrystalline and single crystalline diamond layer. At first the work will be concentrated on design and preparation of detection structures. Following the electrical characterization (current-voltage, capacity-voltage measurements at various temperatures) will be realized. SiC and diamond are wide band gap materials able to work also at increased temperatures. Selected suitable detection structure will be connected to low noise spectrometric set-up and evaluated. Following structures will be irradiated by high doses of radiation (electrons, protons, neutrons) and investigated its properties changes. Finally, the radiation hardness will be evaluated and compared with standardly used silicon detectors.

“Physical Engineering”

  • Theme: Study of thermo – electro – mechanical properties of diamond/GaN heterostructures for high power applications
    Supervisor:  Ing. Tibor Izsák, PhD.   (Department of Microelectronics and Sensors )
    Abstract: Gallium nitride (GaN) electronic devices are in high demand for high-power, high-frequency applications due to their outstanding electronic properties. On the other hand, improved thermal management is necessary for these devices to operate at required power densities with an acceptable lifetime. One solution is to combine the device with a high thermal conductivity material (such as diamond) in the function of heat spreading that can rapidly transfer the localised heat to an external cooling system.
    The PhD work will be focused mainly on the study of the influence of various interlayers (i.e. ~50÷200 nm thin films of SiO2, SixNy, AlN, Al2O3, etc.) on the polycrystalline diamond/GaN heterostructures properties from the point of view of thermal boundary resistance, thermal conductivity, interface charge, mechanical stress. The electrical properties of the realized electronic devices will be investigated by well-known methods (I-V, C-V, radiofrequency). It is supposed that the experimental results will be supported by modelling and simulations. The PhD student will be part of a young research team with international cooperation and with access to high-tech research facilities. The obtained results are highly desired for advanced projects proposals and cooperation with companies.
  • Theme: 3D computer modelling of superconducting power applications
    Supervisor: Mgr. Enric Pardo, PhD.Department of Superconductor Physics )
    Abstract: The goal of this PhD is to develop novel three-dimensional computer modelling methods for superconducting electric power applications, such as motors and generators for electric aircrafts and superconducting magnets. Modelling will be focusses on electro-magnetic and electro-thermal properties. The student will start using our in-house numerical modelling programs and later develop their own. Therefore, skills in general purpose programming languages like C++ and python will be very welcome. Parallel computing strategies will also be explored. The student will benefit from the international collaboration within the framework of the European superEMFL project, with the final goal of designing the superconducitng magnet with the highest magnetic field in Europe, and a European COST action (COST CA19108), aimed to short visits and other international collaboration in the field of superconducting power applications.
  • Theme: Preparation of low-dimensional materials and research of optoelectrical properties for quantum (single-photon) emitters
    Supervisor: Dr. rer. nat. Martin Hulman (Department of Physics and Technology at Nanoscale)
    Abstract: The aim of the project is to investigate the optoelectrical properties of unconventional semiconductors with a wide range of low-dimensional materials for quantum emitters operating in the NIR range at room temperature.
    Designed optically active materials: two-dimensional (2D) heterostructures of graphene and 2D-CuI, 2D-AgI, 2D-BiI3, 2D-NiI2, 2D-SiO2, and nanocrystalline diamond (NCD) doped with Si, N, B, P.
    Preparation: 2D materials will be chemically prepared directly between the graphene layers; encapsulation of a 2D layer in graphene is important for stabilising even 2D structures that do not exist under normal conditions. The diamond structure will be grown on silicon substrates using the microwave-assisted CVD method (MWPECVD). During CVD synthesis, NCDs will be modified with Si, N, B, P dopants at various concentrations.
    Characterisation methods: The atomic configuration of the investigated materials will be studied in close cooperation with the University of Vienna using a scanning transmission electron microscope (STEM) with atomic resolution. The solution of the lattice parameters will enable the calculation of the electronic states of the 2D structures. Photoemission spectra (XPS) and ARPES will be measured in cooperation with the University of Cergy-Paris, where the theoretical electronic structure of the investigated material will be experimentally verified. The optical properties of luminescent microcrystals such as optical gap width, exciton lifetime and quantum emission will be studied by measuring UV-VIS-IR absorption and Raman spectra and photoluminescence and will be correlated with the theoretical structure of electron states. 2D materials that demonstrate significant photoemission at appropriate wavelengths will be selected for the preparation of electronic devices based on 2D heterostructures. The electrical transport of 2D heterostructures and doped NCDs will be measured in the temperature range of 1.5K to 350K. We obtain essential information about optoelectronic properties by measuring the photoconductivity in DC and AC mode and by Hall measurements in a wide range of temperatures.
    The results of the work could significantly contribute to the systematic evaluation of the properties of materials suitable for applications in the field of quantum emitters.
  • Theme: Optimization of the growth of few-layer films of 2D materials and novel heterostructures for application in electronics and advanced sensors
    Supervisor: Mgr. M. Sojková, PhD. (Department of Microelectronics and Sensors )
    Abstract: The discovery of graphene has stimulated an extensive research on other 2D materials. The 2D structure determines the electronic properties that may exhibit correlated electronic phenomena such as charge density waves and superconductivity. Especially transition metal dichalcogenides (TMDs) with the formula MX2, where M is a transition metal (Mo, W, and so on) and X is a chalcogen (S, Se or Te), have attracted much attention due to their layer structure and semiconducting properties. These layered materials exhibit many distinctive characteristics such as outstanding flexibility, moderate carrier mobility and layer dependent electronic and optical properties. This makes TMD materials suitable for various applications such as transparent and flexible field effect transistors (FETs), photodetectors, photovoltaic cells, light-emitting diodes and catalysts. The work will focus on the fabrication of ultra-thin layers of 2D materials, namely reduced graphene oxide (rGO) and transition metal dichalcogenides (TMD). The rGO layers will be deposited by spin-coating. For TMD layers, a two-step method will be used, in which thin layers of metals or their oxides are first deposited by magnetron sputtering or pulsed laser deposition. In the second step, these layers are annealed in the presence of sulfur or selenium vapor (so-called sulfurization / selenization). Several types of TMD (MoS2, PtSe2, PtS2) will be prepared. By combining rGO and TMD layers, new heterostructures will be prepared (e.g. rGO / PtSe2, MoS2 / PtSe2, rGO / MoS2 …). We will study the influence of fabrication parameters on the structural and electrical properties of individual layers and heterostructures. The prepared layers and heterostructures will be investigated by X-ray diffraction analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, optical measurements, electrical properties measurements and other analyzes.
    The work will be carried out at the Institute of Electrical Engineering SAS, which has the necessary technological and characterization equipment. The PhD student will acquire universal skills with a variety of experimental methods and will be actively involved in several projects.

“Physics of Condensed Matter and Acoustics”

  • Theme: Theoretical modeling of spin dynamics in ferromagnetic systems
    Supervisor: Mgr. J. Feilhauer, PhD. (Department of Physics and Technology at Nanoscale)
    Abstract: Nowadays, the trend of miniaturisation of commercial electronics has reached its physical limits. There is an intensive effort to replace the recent silicon technology, based on the electric current as the primary information carrier, with a new paradigm providing a faster and more energy-efficient transport and processing of information than in conventional electronic devices. One of the very promising possibilities is to utilise electron spin as an information carrier which is a keystone of spin electronics (spintronics), a rapidly growing branch of material physics. The spintronic devices are constructed of ferromagnetic materials where the information can be transported in the form of a spin current, spin waves or via topological solitons (e.g. magnetic skyrmions). In our group, we are mainly focused on the theoretical research of transport properties of spin waves in the specifically designed ferromagnetic metamaterials. Due to the topological nature of these metamaterials, the spin waves are localised and channelled in the desired direction. Another subtopic studied in our group is skyrmion creation, stability and manipulation in ferromagnetic dots and layers. Our theoretical tools include an analytical approach, semi-analytical simulations and numerical simulations based on the micromagnetic solver Mumax3 and self-made implementation of metadynamics algorithm. We closely collaborate with several experimental research groups (including those at our institute) and try to verify our numerical predictions by measurements. The aim of this work is to model of static and dynamic properties of magnetic devices of the sub-micron size. The extension of our software capabilities by implementing new algorithms is also expected in this work.
  • Theme: Mesoporous structures functionalization for battery applications
    Supervisor: Ing. B. Hudec, PhD. (Department of Physics and Technology at Nanoscale)
    Co-advisor: doc. RNDr. Martin Moško, DrSc.
    Abstract: A major obstacle for practical implementation of numerous experimental Li-ion battery concepts is the interface degradation between a liquid electrolyte and a mesoporous electrode. Thanks to the electrode’s immense area, the functionalisation of the interface at nano-scale can lead to significant improvement in characteristics of various battery types. The method of choice is the atomic layer deposition (ALD) which allows for homogeneous atomically-thin coatings of material even on substrates of highly complex surface morphology, such as mesoporous (pores 2-50 nm) battery electrodes. The first promising results of using ALD for battery cathodes modification using oxide films several nm thick have been achieved, but a systematic physical analysis of functionalisation mechanisms is still missing.
    The goal of this work will be to understand the mechanism of ALD on highly-structured mesoporous substrates and the physical principle of electrode functionalisation by nano-layers. The research will consist of systematically correlating the functionalisation of commercial mesoporous cathode structures (LFP, NMC…) using ALD with various experimental conditions and the resulting electrical characteristics of such batteries. Evaluation will entail the functionalisation by ultra-thin (units of nm) ALD oxide films (Al2O3, ZnO…) with the utilisation of ex-situ (PALS, SIMS, TEM) and in-situ (RGA, QMS) spectroscopic methods. For correlation of ALD conditions with spectroscopic data, computational fluid dynamics of ALD growth in Autodesk CFD and Ansys Fluid will be used.
    The student will be a part of a research team working on the topic in the frame of ongoing research projects.
  • Theme: Growth and properties of III-N quantum structures for fast electronic
    Supervisor: Ing. J. Kuzmík, DrSc.Department of III-V Semiconductors )
    Co-advisor: Ing. Stanislav Hasenöhrl, Ing. Michal Blaho, PhD.
    Abstract: Topic of the work deals with the growth and investigations of epitaxial III-N quantum structures prepared by metal-organic chemical-vapor deposition. GaN, as a constituting member of III-N family, is a most dynamically developed material in semiconductor industry marked by a Nobel Prize for invention of blue/white LEDs. Presently III-Ns attract a lot of interest also for applications in power, high frequency and automotive electronics.
    Compounds based on III-N (GaN, AlN, InN) and its combinations facilitate preparation of countless heterostructures showing quantum effects. In particular, 2-dimensional charge carrier gas can be created having high density and mobility, which are crucial aspects for future electronic devices. Similarly, InN represents the material with the highest electron drift velocity among all common semiconductors.
    Work will be focused on mastering the growth at the state-of-the-art AIXTRON system. Main emphasize will be given to heterostructure quantum wells containing  In(Al)N for future ultra-fast transistors, as well as preparation of the channel layer based on InN. Material study will include several techniques for structural, electrical and optical investigations. PhD study will be accomplished by processing and demonstration  of test structures and innovative electronic devices.
  • Theme: Preparation of low-dimensional materials and research of optoelectrical properties for quantum (single-photon) emitters
    Supervisor: doc. Ing. V. Skákalová, DrSc. (Department of Physics and Technology at Nanoscale)
    Abstract: The aim of the project is to investigate the optoelectrical properties of unconventional semiconductors with a wide range of low-dimensional materials for quantum emitters operating in the NIR range at room temperature.
    Designed optically active materials: two-dimensional (2D) heterostructures of graphene and 2D-CuI, 2D-AgI, 2D-BiI3, 2D-NiI2, 2D-SiO2, and nanocrystalline diamond (NCD) doped with Si, N, B, P.
    Preparation: 2D materials will be chemically prepared directly between the graphene layers; encapsulation of a 2D layer in graphene is important for stabilising even 2D structures that do not exist under normal conditions. The diamond structure will be grown on silicon substrates using the microwave-assisted CVD method (MWPECVD). During CVD synthesis, NCDs will be modified with Si, N, B, P dopants at various concentrations.
    Characterisation methods: The atomic configuration of the investigated materials will be studied in close cooperation with the University of Vienna using a scanning transmission electron microscope (STEM) with atomic resolution. The solution of the lattice parameters will enable the calculation of the electronic states of the 2D structures. Photoemission spectra (XPS) and ARPES will be measured in cooperation with the University of Cergy-Paris, where the theoretical electronic structure of the investigated material will be experimentally verified. The optical properties of luminescent microcrystals such as optical gap width, exciton lifetime and quantum emission will be studied by measuring UV-VIS-IR absorption and Raman spectra and photoluminescence and will be correlated with the theoretical structure of electron states. 2D materials that demonstrate significant photoemission at appropriate wavelengths will be selected for the preparation of electronic devices based on 2D heterostructures. The electrical transport of 2D heterostructures and doped NCDs will be measured in the temperature range of 1.5K to 350K. We obtain essential information about optoelectronic properties by measuring the photoconductivity in DC and AC mode and by Hall measurements in a wide range of temperatures.
    The results of the work could significantly contribute to the systematic evaluation of the properties of materials suitable for applications in the field of quantum emitters.
  • Theme: Observation of noncolinear magnetic states at nanoscale

    Supervisor: Ing. J. Šoltýs, PhD. (Department of Physics and Technology at Nanoscale)
    Co-advisor: Dr. Michal Mruczkiewicz
    Abstract: Over the last decade, there has been a significant improvement in the recording density and speed of storage media. However, developments are constantly growing, and the next concepts for new memories are being researched to meet the requirements for miniaturisation, energy efficiency and transfer rate. Magnetic nanostructures are candidates for novel information carriers and storage that could go beyond the limits of semiconductor technology. Advanced application concepts often rely on noncolinear magnetic state presence [1]. In this work, a student will employ recent numerical tools  (mumax, OOMMF, Comsol) to study noncolinear magnetic states and their applications. He/she will learn fabrication techniques to prepare patterned micro-nano structures hosting noncolinear magnetic states and employ detection methods to confirm the presence of spin dynamics of magnetic texture.
    [1] Mruczkiewicz, Michal, and Pawel Gruszecki. “The 2021 roadmap for noncollinear magnonics.” Solid State Physics. Vol. 72. Academic Press, 2021. 1-27.