Themes of PhD Thesis

“Electronics and photonics”

  • 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: InAl(Ga)N/GaN RF transistors for next generation of mixed-signal electronics 

    Supervisor: Ing. J. Kuzmík, DrSc.Department of III-V Semiconductors )
    Co-advisors:  Ing. M. Blaho, PhD.,  RNDr. D. Gregušová, DrSc.
    Abstract: Mixed-signal integrated circuits, processing both analog and digital signals on one chip, are being widely used in modern electronics (e.g. in telecom and consumer electronics). Owing to its unique properties, GaN based heterostructure transistor technology offers preparation of RF as well as digital transistors operating at much higher frequencies compared to Si based systems. However, further research and development is necessary for integration of both modules. The PhD study will aim development of the processing technology for RF transistors employing InAl(Ga)N/GaN heterostructure, which allows drastic scaling of the barrier thickness. To minimize the switching time of the transistors, the gates will be defined using direct electron lithography. DC and pulsed measurements will be employed to study and supress the transistor’s parasitic effects. In cooperation with international partner providing RF measurements, the electron transport in the transistor‘s intrinsic part will be studied in order to suppress the undesired sources of delays and maximize cut-off frequency and maximum oscillation frequency (ft and fmax) of the RF devices.

  • Theme: Development and characterization of pn heterojunction based on ultra-wide-bandgap semiconductors

    Supervisor: Ing. Milan Ťapajna, PhD.Department of III-V Semiconductors )
    Abstract: Current electronic power device market is mostly covered by Si (<1kV voltage range) and SiC and GaN (up to several kV). At present, however, there are practically no semiconductor power devices available for the 10-kV range. Gallium oxide (Ga2O3) is a novel and promising ultra-wide bandgap (Eg=4.8–5.3 eV) semiconductor material, which offer technological potential for design of new electronic devices for 10-kV range. Such devices can enable development of systems for transportation utilising electric drive (cars, trains, ships, aircrafts) or high-voltage transformation in future low-loss DC power distribution networks. However, besides other issues, development of Ga2O3 power devices is hampered mainly by inefficient p-type doping required in typical power device designs. This work aims the development of full metal-oxide heterojunction based on Ga2O3 and naturally p-type metal-oxides including NiO and Cu2O for pn heterojunction. This includes optimisation of growth technologies for the used materials, development of pn heterojunction processing, and detail characterisation of their electrical and electro-optical properties. For this purpose, state-of-the-art technologies and characterisation methodologies available at IEE SAS will be employed.
  • Theme: Influence of technology on the material properties of wide bandgap semiconductors and self-heating of related devices

    Supervisor: Ing. Milan Ťapajna, PhD.Department of III-V Semiconductors )
    Co-advisor: Ing. Filip Gucmann, PhD.
    Abstract: Current semiconductor material research for next-generation electronic devices shows an on-going long-time interest in materials with bandgap energies (Eg) exceeding that of Si. While GaN and SiC have long time been materials of choice, other candidates such as high-Al content AlGaN, diamond, and Ga2O3 are becoming increasingly more attractive for high voltage/high power applications. Owing to a relatively simple synthesis of bulk crystals and epitaxial layers, ultrawide bandgap (Eg~4.8-5.4eV), and high theoretical breakdown field (Ebr~8MV/cm), Ga2O3 is a very promising material for high reverse blocking voltage (>8KV) electronic devices and eventually for high-power switching. The key material issue of Ga2O3 is low and anisotropic thermal conductivity (κ~10-27W/mK pre β-Ga2O3), which will a have critical influence on self-heating and reliability of manufactured devices. It is therefore very desirable, to study effects of device self-heating influenced by the technology of Ga2O3 growth, e.g. effect of various crystal phases of Ga2O3 and thermal conductivity of used substrate material. The focus of this thesis will be a systematic investigation of the Ga2O3 material properties influenced by the technology of epitaxial growth, developing a Ga2O3 device processing technology, and following detailed electrical, optical, and thermal characterisation. A significant effort will be devoted to detailed characterisation of epitaxial layers and devices manufactured from Ga2O3 grown on high thermal conductivity substrates, e.g. SiC aimed for better dissipation of device generated waste heat. For this study, we will use modern technological equipment and methods, available at the Institute of Electrical Engineering, SAS and Institute of Physics, SAS.
  • Theme: Energy harvesters based on advanced materials for MEMS sensor applications

    Supervisor: Ing. Gabriel Vanko, PhD. (Department of Microelectronics and Sensors )
    Abstract: Sensors are part of our everyday life and can be found in common electronic devices (e.g. smartphones) or in devices for health/environment monitoring. Autonomous sensors can be percieved as sensing elements capable of independent and wireless operation over a relatively long time period without need of an external power supply system that can be replaced by a battery powered by an energy harvester. Energy harvesting is currently one of the least explored application areas of microelectromechanical systems (MEMS) based on a group of III-nitride semiconductor materials (III-N). The concept of piezoelectric MEMS energy harvesters based on AlGaN/GaN heterostructures is highly challenging in terms of optimizing the charge conversion efficiency. In this area, the possibilities of using materials with high values of piezoelectric coefficients (ZnO, PZT, 2D materials from the group of monochalcogenides, etc) will be discussed. The thesis will be focused on a.) synthesis of structures and devices; b.) investigation of their mechanical and electronic properties; c.) study of the possibilities of their integration into existing MEMS concepts. Due to the complexity of the topic, the thesis can be formulated from the point of view of technology (proposing and performing processing technology steps), characterization (proposing and performing measurement techniques) or simulation (proposing electro-physical models of structures and devices).
  • Theme: Preparation and study of semiconductor detectors of ionizing radiation based on GaAs and SiC materials

    Supervisor: Mgr. Bohumír Zaťko, PhD. (Department of Microelectronics and Sensors )
    Abstract: The aim of the thesis is technology preparation of ionizing detectors, study of electrical and detection properties and interpretation of obtained results. Used detection materials are semi-insulating GaAs and high quality epi-layer of 4H-SiC. At first the work will be concentrated on design and preparation of detection structures. Following the electrical characterization (current-voltage, capacity-voltage measurements) will be realized. Selected suitable detection structure can be conneted to spectrometric set-up. The optimalization in term of noise should be perfomed according to detector characteristics (reverse current in operation point, value of capacity). Finally the detection and spectrometric properties will be evaluated.

“Physical Engineering”

  • Theme: Manufacture and properties of MgB2 superconducting joints  aimed for coils in persistent mode

    Supervisor: Ing. P. Kováč, DrSc.  ( Department of Superconductor Physics )
    Co-advisor: Ing. Ján Kováč, PhD.
    Abstract: Advanced superconding systems are using windings working in so called persistent mode, which allows to improve the stability of generated fields as well as to lowered energy for cooling. Therefore, the topic of this PhD work is focussed to preparation of superconducting joints and their properties aiming to reach joint current at least 50% of critical current of the reference wire. Superconducting joints will be prepared for MgB2 wires made by different techniques (ex-situ, in-situ a IMD). Structural studies will be analysed by electron and optical microscopy and joint transport current performed at 4.2 K and external magnetic fields 0-8T. The superconducting joint having the best performance will be used for small model coil working in persistent mode and in-time field stability will be monitored by Hall probe.
  • Theme: Multi-physics modelling of superconducting power and magnet applications

    Supervisor: Mgr. Enric Pardo, PhD.Department of Superconductor Physics )
    Abstract: The main task of this PhD will be to develop novel multi-physics numerical modeling methods for superconducting applications regarding low-frequency electro-magnetic, electro-thermal and electro-mechanical properties. We are currently working on several international and national projects regarding motors and generators for hybrid and electric aircraft or high-field magnets. The student will further develop our in-house numerical modeling programs (and possibly make some new from their own). Then, we will value positively knowledge in programming languages like C++ or python, but we may also offer training in this aspect. 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 an European COST action (COST CA19108), aimed to short visits and other international collaboration in the field of superconducting power applications.
  • Theme: Study of thermo – electro – mechanical properties of diamond/GaN heterostructures for high power applications

    Supervisor: Ing. Gabriel Vanko, PhD. (Department of Microelectronics and Sensors )
    Co-advisor: Ing. Tibor Izsák, PhD.
    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: Crystal optics for high resolution X-ray imaging

    Supervisor: Mgr. Bohumír Zaťko, PhD. (Department of Microelectronics and Sensors )
    Co-advisor: Ing. Zdenko Zápražný, PhD.
    Abstract: High resolution X-ray imaging in real or reciprocal space requires high resolution X-ray optics, which effectively increases the resolution (spatial or spectral) and also transmits sufficiently X-ray beam intensity. The work will be focused mainly on X-ray optics performing expansion or focussing of the X-ray beam in one (1D) to three dimensions (2D, 3D) without an image distortion. A perfect surface planarity and reduced roughness is of paramount importance in advanced X-ray metrology or X-ray imaging, where the angle of incident or diffracted X-ray beams is very low, the examples being grazing incidence monochromators and X-ray magnifiers. The shape of monochromator has to be designed with functional surfaces open for modern finishing methods as nano-machining and post-polishing. Prior to the production of X-ray optical element, ray tracing simulations and proposing the optimal design for a specified application will be needed. High resolution diffractometer and AFM microscope will be used for characterization of the quality of active optical surfaces (roughness, planarity, subsurface damage). Testing of imaging or focusing ability will be done mostly using high intensity laboratory sources in combination with other optical elements and detectors based on direct converting Medipix camera with silicon or GaAs chip, which are in our department also developed and tested.

 

“Physics of condensed matter and acoustics”

  • Theme: Growth and properties of III-N quantum structures for fast electronic

    Supervisor: Ing. J. Kuzmík, DrSc.Department of III-V Semiconductors )
    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.
    The 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.