Diploma Thesis

  • Title: GaN-based heterostructure as a promising sensor for space application
    Supervisor: Ing. Roman Stoklas, PhD. (Dpt. III-V Semiconductors IEE SAS)
    Ing. Martin Florovič, PhD. (ÚE FEI STU)
    Stud. Programma: Electronics and Photonics
    Abstract:
    In the recent years, high-speed photodetectors have received much attention. The metal-semiconductor-metal (MSM) photodetector can be easily implemented in an unmodified MESFET or HFET technology. Fundamentally, the MSM photodetector is comprised of a pair of biased interdigitated metallization on a semiconductor surface. The metal-to-semiconductor interfaces form Schottky or rectifying contacts. The combination of the two Schottky contacts create a low noise and highly sensitive photodetector. The MSM Schottky barrier diodes are attractive high-speed photodetectors because of their low dark current, fast response, superior responsivity and direct compatibility with modern high-speed integrated circuitry.
    Generally, decreasing the spacing between diode fingers will decrease transit time of the carriers and detector response. The spectral responsivity of the detector is primarily a function of the substrate material band gap. Device operating speed is dependent on electrode geometry as well as substrate characteristics such as electron and hole motilities. Dark current is dependent on the characteristics of the rectifying contacts formed between the electrode metals and the substrate material. The main advantage of GaN-based sensor is the radiation hardness in the space compare to Si and GaAs-based structures. In principle, the different transparent conductors like as thin metal electrodes and/or ITO deposited on an active area, could be also investigated.
  • Title: Temperature dependent of high resistivity semiconductor on InAlN:Mg-based structures using Van der Pauw and Hall measurement techniques
    Supervisor: Ing. Roman Stoklas, PhD. (Dpt. III-V Semiconductors IEE SAS)
    Ing. Martin Florovič, PhD. (ÚE FEI STU)
    Stud. Programma: Electronics and Photonics
    Abstract:
    Semiconductors have high resistivity in the mega-ohm range and special methods are required to avoid contact and isolation resistances, as well as voltage and temperature effects. The InAlN-based structures doped by Mg are used as buffer layer for HFET transistors with InN channel. The main reason is to reduce a high electron concentration accumulated on the surface of InAlN. As a p-doping in combination with n-type InAlN, the structures compatible with CMOS technology can be prepared. The four-point method and Van der Pauw techniques are normally used for the resistivity measurement of doped structures. Conductivity type, mobility and measurement of a bulk and sheet doping concentration can be simply analysed by the Hall measurement. However, for high resistive material, the carrier respond to magnetic field is limited by small carrier mobility. Therefore, Hall measurement using AC signal (AC Transport technique) are used instead of DC-Van der Pauw method.
    The main aims of the diploma thesis will by an understanding of the basic principles of measurement techniques.  In addition, temperature dependent tests of devices can help us to investigate the high resistive samples, where the characterization at room temperature is very difficult.
  • Title: Development and characterization transistors based on ultra-wide-bandgap Ga2O3 semiconductor
    Supervisor: Ing. M. Ťapajna, PhD. ( Dpt. III-V Semiconductors IEE SAS)
    doc. Ing. Miroslav Mikolášek, PhD. (ÚE FEI STU)
    Stud. Programma: Electronics and Photonics
    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 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 transformation for high-voltage DC power distribution networks. Currently, great research effort is focused to growth of Ga2O3 and development of related electronic devices for power application. This work aims the processing and characterization of transistors based on Ga2O3 films grown by chemical vapor deposition at IEE SAS. A student will be involved in the transistor processing using state-of-the-art technologies and electrical characterization of prepared devices. The gained knowledge will be used for further optimization of Ga2O3 growth technology.
  • Title:Morphology, electrical, and optical properties of the ultrawide bandgap semiconducting Ga2O3 layers prepared by the metalorganic chemical vapour deposition
    Supervisor: Ing. Filip Gucmann, PhD. ( Dpt. III-V Semiconductors IEE SAS)
    doc. Ing. Miroslav Mikolášek, PhD. (ÚE FEI STU)
    Stud. Programma: Electronics and Photonics
    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 gallium oxide (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 ~5 eV), and high theoretical breakdown field (Ecr ~8 MV/cm), Ga2O3 is a very promising material for high reverse blocking voltage (>8 kV) electronic devices and eventually for high-power switching. Such devices can enable and accelerate development of electric means of transportation or high-voltage DC-DC voltage levels conversion systems for future low-loss DC power distribution networks.
    The scope of this work covers a study of surface morphology, electrical, and optical properties of Ga2O3 layers prepared at the Institute of Electrical Engineering, SAS by metalorganic chemical vapour deposition by means of atomic force microscopy and suitable electrical and optical methods (e.g. van der Pauw, optical absorption/transmittance, Raman spectroscopy). Valuable findings acquired during this Master thesis will contribute to the optimisation of the epitaxial growth of Ga2O3 layers and development of new electronic devices. For this study, we will use modern technological equipment and methods, available at the Faculty of Electrical Engineering and Information Technology STU, Institute of Electrical Engineering SAS, and Institute of Physics SAS.
  • Title: Digital etching in the processing of semiconductor devices
    Supervisor: RNDr. Dagmar Gregušová, DrSc. ( Dpt. III-V Semiconductors IEE SAS)
    doc. Ing. Jaroslav Kováč, PhD. (ÚE FEI STU)
    Stud. Programma: Electronics and Photonics
    Abstract:
    Processing of III-V and III-N based semiconductor devices is associated with many partial tasks, that are very effective and important for the preparation of the device as well as its high-quality functioning. One of the processes is also the digital etching.
    The digital etching is a very fine subtraction of material. The process consists of repeating cycles of a surface oxidation in oxygen plasma and a subsequent etching of the created oxide layer. The result of a sufficiently many cycles is the etching of a very thin semiconductor layer.
    Student will prepare a testing sample, where the digital etching will be investigated. Oxidation and etching parameters will be adjusted. The efficiency of the process and the quality of the etched surface will be evaluated from the Atomic Force Microscopy (AFM) measurements.
    Optimised parameters of the digital etching will be applied for etching under the gate electrode in a High Electron Mobility Transistor (HEMT).
  • Title:Effect of the semiconductor surface processing on the properties of III-V based MOS structures
    Supervisor: RNDr. Dagmar Gregušová, DrSc. ( Dpt. III-V Semiconductors IEE SAS)
    doc. Ing. Jaroslav Kováč, PhD. (ÚE FEI STU)
    Stud. Programma: Electronics and Photonics
    Abstract:
    Surface of the semiconductor has an important role in the preparation of devices, as shown by the research of surfaces on the III-V and III-N semiconductors. It is necessary to eliminate the unwanted effect of the semiconductor surface on the device parameters.
    Aim of the thesis is to determine the effect of surface processing before an oxide layer deposition in a metal-oxide-semiconductor (MOS) heterostructure. Different types of etching will be applied: wet etching in HCl and HF to remove natural oxide and digital etching, which is a cycle of surface oxidation and subsequent etching of the created oxide.
    Student will measure IV and CV characteristics on the prepared samples to determine the effect of etching on the parameters of high electron mobility transistors (HEMTs).
  • Title: Preparation and study of properties of ultra-thin layers and structures of 2D materials
    Supervisor: Mgr. M. Sojková, PhD. ( Dpt. Microelectronics and Sensors IEE SAS)
    doc. Ing. Miroslav Mikolášek, PhD. (FEI STU)
    Stud. Programma: Physical engineering
  • Title: Transistor structures based on ultrathin PtSe2 layers
    Supervisor: Mgr. M. Sojková, PhD. ( Dpt. Microelectronics and Sensors IEE SAS)
    doc. Ing. Miroslav Mikolášek, PhD. (FEI STU)
    Stud. Programma: Electronics and Photonics
  • Title: Microstructure characterisation of Ga2O3 layers for new ultra-wide-bandgap semiconductor electronic devices
    Supervisor: Ing. Rosová Alica, CSc. ( Dpt. Superconductors IEE SAS)
    Prof. Ing. Peter Ballo, PhD. (ÚJFI FEI STU)
    Stud. Programma: Physical engineering
    Abstract:
    Gallium oxide (Ga2O3) is a promising ultra-wide bandgap (Eg ~5 eV) semiconductor material, which offers technological potential for design of new electronic devices for 10-kV range, practically unavailable at the present time. Such devices can enable and accelerate development of electric means of transportation or high-voltage DC-DC voltage levels conversion systems for future low-loss DC power distribution networks.
    The scope of this work covers a microstructure study of Ga2O3 layers prepared at the Institute of Electrical Engineering, SAS by chemical vapour deposition using various electron microscopy techniques. This study will provide a feedback for optimisation of Ga2O3layers growth and their electrical, and electro-optical properties required for the manufacture of rectifying metal/semiconductor or heterostructure pn diodes and transistors based on Ga2O3.
  • Title: Microstructure of InAlN semiconducting layers deposited using metalo-organic chemical vapour deposition
    Supervisor: Ing. Rosová Alica, CSc. ( Dpt. Superconductors IEE SAS)
    Prof. Ing. Peter Ballo, PhD. (ÚJFI FEI STU)
    Stud. Programma: Physical engineering
    Abstract:
    Thanks to exceptional properties of GaN-based semiconductors, electronic devices made of their heterostructures can work at significantly higher frequencies as those fabricated using Si-based technology. Preparation of epitaxial ternary compounds with required quality is much more complicated and it needs their microstructure screening control. It is the knowledge of microstructure state and various defects presence control which can reveal relations between electric properties of these heterostructures and their preparation technology.
    The aim of this work is microstructural characterization of InAlN layers deposited at Institute of Electrical Engineering SAS by metal-organic chemical vapour deposition using various techniques of electron microscopy including scanning electron microscopy and transmission electron microscopy.