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  • Author: Jaroslav Kováč x
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Jaroslav Kováč, Martin Florovič, Andrej Vincze, Edmund Dobročka, Ivan Novotný, Miroslav Mikolášek and Jaroslava Škriniarová

Abstract

The present work reports the fabrication of p-Si/SiO2 /TiO2 and p-Si/SiO2 /TiO2 /ZnO heterostructures deposited by RF sputtering on p-Si substrate. The structural properties of the heterostructures were characterized by X-ray reflectivity and SIMS depth profiling. The electrical and optical properties of the heterostructures were investigated by I − V, C-V measurements and VIS spectroscopy, respectively. The measurements reveal that I − V characteristics in dark show semiconductor-insulator-semiconductor (SIS) structure properties. The I − V characteristics under illumination exhibit changes with significant increase of photocurrent due to photoassisted tunnelling and injection through SiO2 /TiO2 interlayer.

Open access

Martin Florovič, Róbert Szobolovszký, Jaroslav Kováč, Jaroslav Kováč, Aleš Chvála, Jean-Claude Jacquet and Sylvain Laurent Delage

Abstract

GaN-based HEMTs’ high potential is deteriorated by self-heating during the operation, this has influence on the electrical properties as well as device reliability. This work is focused on an average channel temperature determination of power AlGaN/GaN HEMT prepared on SiC substrate using quasi-static and pulsed I-V characterization. There was analyzed the drain current change relation to temperature dependent electrical HEMT parameters such as source resistance, threshold voltage, saturation velocity, resp. leakage current which allows to calculate an average channel temperature versus dissipated power for various ambient temperature. Differential temperature of investigated device with and without heatsink was determined. Obtained results were discussed using simulated spatial temperature distribution.

Open access

Rudolf Kinder, Miroslav Mikolášek, Daniel Donoval, Jaroslav Kováč and Marek Tlaczala

One of the biggest challenges of communication networks is the video transmission in real time. It requires high demands on the available network capacity and transport mechanisms. Availability of smart mobile devices with batteries, which keep the terminal working for several hours, caused an increased interest in the research of the deployment of video transmission in wireless transmission systems. The presented paper deals with the transmission of video encoded with H.264/AVC (Advanced Video Coding) video coding standard through wireless local area network (WLAN) using the programming environment OPNET Modeller (OM). The test network studied in this work was prepared by combining real and simulated networks, which allows interesting possibilities when working with the OM tools. Such an approach to working with OM allows a detailed video streaming analysis, because the video output was noticeably not only in the form of statistics, but we can see the real impact of transmission failures. Using the OM simulation environment allows to design the transmission systems, which would be difficult to establish in laboratory conditions.

Open access

Pavol Hronec, Jaroslava Škriniarová, Anna Benčurová, Pavol Nemec, Dušan Pudiš and Jaroslav Kováč

Abstract

The paper deals with optical characterization of the Al0.295Ga0.705As/GaAs multi-quantum well light emitting diode (LED) structure with photonic crystal (2D PhC) patterned on the top of the structure using Electron Beam Direct Write Lithography (EBDWL). Light-current characteristics measured by integrating sphere shows increase of extracted light intensity as 21.1%. Additionally, extracted light intensity was studied by far-field measurements as a complementary method to light-current characteristics. The far-field measurements show increase of extracted light intensity as 31.2%. We suggest this method as more suitable for evaluation of extracted light intensity because it omits emission from edges of the LED and thus light is measured only from the area where PhC is patterned

Open access

Miroslav Mikolášek, Michal Nemec, Jaroslav Kováč, Ladislav Harmatha and Lukáš Minařík

Abstract

In this paper we present the utilization of capacitance and current-voltage diagnostic techniques to analyse silicon heterojunction solar cell structures properties, particularly focused on the inspection of the amorphous emitter and amorphous silicon/crystalline silicon hetero-interface. The capacitance characterization of investigated samples have revealed the need for improvement of the a-Si:H/c-Si heterointerface quality as a main direction to obtain superior output performance of heterojunction cells. In addition, current-voltage characterization emphasized importance for enhancement of the light management in the structure. The obtained results demonstrate that electrical and capacitance diagnostic techniques can represents important diagnostic tools in the process of optimization of solar cells.

Open access

Martin Florovič, Jaroslav Kováč, Peter Benko, Aleš Chvála, Jaroslava Škriniarová and Peter Kordó

Abstract

Electrical properties of recessed and non-recessed AlGaN/GaN Schottky diodes under off-state stress were investigated. The samples were consecutively stressed by the stepped negative bias (−60 V). Before and after the stress I−V and C−V characteristics were evaluated to verify the device degradation process. Finally, the degradation mechanism and the influence of AlGaN recessed layer thickness on the electrical properties of the Schottky diodes were analysed. It was found that the short time stress influence on I−V characteristics was most negligible for the non-recessed sample. Shallow and deep recessed samples exhibited initial trap filling and reverse current decrease. Generally it was found that the stress voltage near 60 V caused recoverable device degradation

Open access

Damian Pucicki, Katarzyna Bielak, Beata Ściana, Wojciech Dawidowski, Karolina Żelazna, Jarosław Serafińczuk, Jaroslav Kováč, Andrej Vincze, Łukasz Gelczuk and Piotr Dłużewski

Abstract

GaInNAs alloys are mostly used as an active part of light sources for long wavelength telecom applications. Beside this, these materials are used as thin quantum wells (QWs), and a need is to grow thick layers of such semiconductor alloys for photodetectors and photovoltaic cells applications. However, structural characterization of the GaInNAs layers is hindered by non-homogeneity of the In and N distributions along the layer. In this work the challenges of the structural characterization of doped thick GaInNAs layers grown by atmospheric pressure metalorganic vapour phase epitaxy (APMOVPE) will be presented

Open access

Arád Kósa, L’ubica Stuchlíková, Wojciech Dawidowski, Juraj Jakuš, Beata Sciana, Damian Radziewicz, Damian Pucicki, Ladislav Harmatha, Jaroslav Kováč and Marek Tłaczala

Abstract

In this paper authors present the results of identification of emission and capture processes in tandem solar cell structures based on quaternary InGaAsN semiconductor alloys by DLTFS (Deep Level Transient Fourier Spectroscopy) and by ana- lytical evaluation processes. The energies of five trap levels ET1=0.77 eV, ET2=0.47 eV, ET3=0.64 eV, HT1=0.62 eV and HT2=0.53 eV were identified with reliable accuracy. These values were obtained by available analytical procedures, verified by simulations and confirmed by reference structures with basic layer types and compared with possible reference trap data. Native structural defects in GaAs were stated as the origin of these deep energy levels

Open access

Wojciech Dawidowski, Beata Šciana, Iwona Zborowska-Lindert, Miroslav Mikolášek, Magdalena Latkowska, Damian Radziewicz, Damian Pucicki, Katarzyna Bielak, Mikołaj Badura, Jaroslav Kováč and Marek Tłaczała

Abstract

Tandem (two p-n junctions connected by tunnel junction) and multijunction solar cells (MJSCs) based on AIIIBV semiconductor compounds and alloys are the most effective photovoltaic devices. Record efficiency of the MJSCs exceeds 44% under concentrated sunlight. Individual subcells connected in series by tunnel junctions are crucial components of these devices. In this paper we present atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE) of InGaAsN based subcell for InGaAsN/GaAs tandem solar cell. The parameters of epitaxial structure (optical and electrical), fabrication process of the test solar cell devices and current-voltage (J-V) characteristics are presented and discussed.