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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

Miroslav Mikolášek, Ján Jakaboviš, Vlastimil Řeháček, Ladislav Harmatha and Robert Andok

Abstract

In this paper we present the capacitance study of the intrinsic amorphous silicon/crystalline silicon heterostructure with the aim to gain insight on the heterointerface properties of a passivated silicon heterojunction solar cell. It is shown that due to the high density of defect states in the amorphous layer the structure has to be analyzed as a heterojunction. Using the analysis, the following values have been determined: conduction-band offset of 0.13 eV, electron affinity of 3.92 eV, and density of defect states in the intrinsic amorphous silicon being that of 4.14 X 1021m—3.

Open access

Juraj Racko, Miroslav Mikolášek, Peter Benko, Ondrej Gallo, Ladislav Harmatha, Ralf Granzner and Frank Schwierz

Coupled Defect Level Recombination in the P—N Junction

The well known Shockley-Read-Hall (SRH) model considers emission and capture processes at defects exhibiting a single level or multiple non-coupled levels in the band gap of the semiconductor. The present paper generalizes the model to the case of two mutually coupled defect levels acting as trapping centres. If the intercenter transition is not considered, the model reduces to the case of two non-coupled levels treated by the SRH model.

Open access

Milan Perný, Vladimír Šály, Michal Váry, Miroslav Mikolášek, Jozef Huran and Juraj Packa

Abstract

The amorphous silicon carbide/crystalline silicon heterojunction was prepared and analyzed. The current-voltage (I − V ) measurements showed the barrier properties of prepared sample. Biased impedance spectra of Al/a-SiC/c-Si(p)/Al heterojunction under the standard illumination are reported and analyzed. AC measurements in the illuminated conditions were processed in order to identify electronic behavior using equivalent AC circuit which was suggested and obtained by fitting the measured impedance data. A phenomenon of negative capacitance/resistance in certain frequency range has been observed.

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

Liday Jozef, Vogrinčič Peter, Vretenár Viliam, Kotlár Mário, Marton Marián, Mikolášek Miroslav and Řeháček Vlastimil

Abstract

We have designed and verified a new structure for ohmic contacts to p-GaN based on a layer of carbon nanotubes (CNT), reduced graphene oxide (r-GO) and metallic layers of Cr, Pd and Au, namely in configurations Au/Cr/r-GO/CNT/p-GaN and Au/Pd/r-GO/CNT/p-GaN. The effects have been studied of the annealing temperature and the gas ambient upon the electrical properties of the contacts. Annealing of the Au/Pd/r-GO/CNT/p-GaN structure in air at 500°C for 1 minute resulted in linear I - V curves measured between planar electrodes on the p-GaN. Hence, addition of r-GO to the CNT interlayer between p-GaN and the metallization layer is a highly promising procedure for further improvements of the ohmic contacts to p-GaN.

Open access

Milan Perný, Vladimír Šály, František Janíček, Miroslav Mikolášek, Michal Váry and Jozef Huran

Abstract

Due to the particular advantages of amorphous silicon or its alloys with carbon in comparison to conventional crystalline materials makes such a material still interesting for study. The amorphous silicon carbide may be used in a number of micro-mechanical and micro-electronics applications and also for photovoltaic energy conversion devices. Boron doped thin layers of amorphous silicon carbide, presented in this paper, were prepared due to the optimization process for preparation of heterojunction solar cell structure. DC and AC measurement and subsequent evaluation were carried out in order to comprehensively assess the electrical transport processes in the prepared a-SiC/c-Si structures. We have investigated the influence of methane content in deposition gas mixture and different electrode configuration.

Open access

Ladislav Harmatha, Miroslav Mikolášek, L’ubica Stuchlíková, Arpád Kósa, Milan Žiška, Ladislav Hrubčín and Vladimir A. Skuratov

Abstract

The contribution is focused on the diagnostics of structures with a heterojunction between amorphous and crystalline silicon prepared by HIT (Heterojunction with an Intrinsic Thin layer) technology. The samples were irradiated by Xe ions with energy 167 MeV and doses from 5 × 108 cm−2 to 5 × 1010 cm−2. Radiation defects induced in the bulk of Si and at the hydrogenated amorphous silicon and crystalline silicon (a-Si:H/c-Si) interface were identified by Deep Level Transient Spectroscopy (DLTS). Radiation induced A-centre traps, boron vacancy traps and different types of divacancies with a high value of activation energy were observed. With an increased fluence of heavy ions the nature and density of the radiation induced defects was changed.

Open access

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

Arpád Kósa, Miroslav Mikolášek, Ľubica Stuchlíková, Ladislav Harmatha, Wojciech Dawidowski, Beata Ściana and Marek Tłaczała

Abstract

This paper is dedicated to electro-physical characterisation of a GaAs p-i-n structure grown for solar cell applications, which was carried out by light and dark current-voltage (IV) and Deep Level Transient Fourier Spectroscopy (DLTFS) methods. The conversion efficiency and open-circuit voltage were determined from IV measurement at 1 and 20× sun light concentrations. Three electron like defects TAn1, TAn2, TDn and one hole like defect TBp obtained by DLTFS measurements were confirmed. The origin of these defect states was stated as native GaAs impurities.