J. Soltys

Slovak Academy of Sciences, Bratislava, Bratislavsky Kraj, Slovakia

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Publications (14)13.71 Total impact

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    ABSTRACT: We have investigated the magnetization properties and flux dynamics of superconducting Cu$_x$TiSe$_2$ single crystals within wide range of copper concentrations. We find that the superconducting anisotropy is low and independent on copper concentration ($\gamma\sim1.7$), except in the case of strongly underdoped samples ($x\leq0.06$) that show a gradual increase in anisotropy to $\gamma\sim1.9$. The vortex phase diagram in this material is characterized by broad region of vortex liquid phase that is unusual for such low-$T_c$ superconductor with low anisotropy. Below the irreversibility line the vortex solid state supports relatively low critical current densities as compared to the depairing current limit ($J_c/J_0\sim10^{-7}$). All this points out that local fluctuations in copper concentration have little effect on bulk pinning properties in this system.
    Physical Review B 10/2013; · 3.66 Impact Factor
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    ABSTRACT: We have used micro-Hall probe for the study of vortex dynamics in micromagnetic objects with lowered symmetry. The Pacman-like nanodot of the diameter of 1 μm was placed directly on the Hall probe and the signal was red in band resistance configuration. We show that the vortex nucleation and annihilation, as well as s-and c-state creation/annihilation are clearly visible on the magnetization reversal characteristics at 77 K. The experimental characteristics is in good agreement with the one calculated by micromagnetic simulations.
    Advanced Semiconductor Devices & Microsystems (ASDAM), 2012 Ninth International Conference on; 01/2012
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    ABSTRACT: Micrometer-scaled cantilever-based sensors can be utilized in electrostatic and magnetic measurements and also are perspective for future chemical and biological sensing applications. GaAs is the most used III-V material for cantilever probe development thanks to its optoelectronic properties, high mobility 2D electrons, high piezoresistivity and sufficient mechanical properties. Novel sensing probes, prepared by integration of various detection elements are perspective for specific requirements. This work is mainly focused on technology process of such micro-CLs and also on fabrication of detection elements (transistors) with the aim to integrate directly on the micro-CLs.
    Advanced Semiconductor Devices & Microsystems (ASDAM), 2012 Ninth International Conference on; 01/2012
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    ABSTRACT: The local anodic oxidation (LAO) by the tip of atomic force microscope (AFM) is used for fabrication of nanometer-scaled structures and devices. We study the technology of LAO applied to semiconductor heterostructures, theoretically and experimentally as well. The goal is to improve the LAO process itself, i.e., to create narrow LAO lines that form high-energy barriers in the plane with the 2D electron gas. In the first part we show the electric field distribution in the system tip-sample during LAO. For samples with low-conductive cap layer the maximum electric field is shifted apart the tip apex, which leads to wide oxide lines. Our Monte Carlo (MC) calculations show how the height of the energy barrier in the system depends on the geometry of the created lines (trenches), and on voltage applied to the structure. Based on the calculations, we have proposed a novel LAO technology and applied it to InGaP/AlGaAs/GaAs heterostructure with doping layer only 6 nm beneath the surface. The doping layer can be oxidized easily by the AFM tip in this case, and the oxide objects can be removed by several etchants. This approach to the LAO technology leads to narrow LAO trenches (approximately 60 nm) and to energy barriers high enough for room- and low-temperature applications.
    Ultramicroscopy 06/2008; 108(10):1021-4. · 2.47 Impact Factor
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    ABSTRACT: We have experimentally explored a new approach to local anodic oxidation (LAO) of a semiconductor heterostructures by means of atomic force microscopy (AFM). We have applied LAO to an InGaP/AlGaAs/GaAs heterostructure. Although LAO is usually applied to oxidize GaAs/AlGaAs/GaAs-based heterostructures, the use of the InGaP/AlGaAs/GaAs system is more advantageous. The difference lies in the use of different cap layer materials: Unlike GaAs, InGaP acts like a barrier material with respect to the underlying AlGaAs layer and has almost one order of magnitude lower density of surface states than GaAs. Consequently, the InGaP/AlGaAs/GaAs heterostructure had the remote Si-delta doping layer only 6.5 nm beneath the surface and the two-dimensional electron gas (2DEG) was confined only 23.5 nm beneath the surface. Moreover, InGaP unaffected by LAO is a very durable material in various etchants and allows us to repeatedly remove thin portions of the underlying AlGaAs layer via wet etching. This approach influences LAO technology fundamentally: LAO was used only to oxidize InGaP cap layer to define very narrow (approximately 50 nm) patterns. Subsequent wet etching was used to form very narrow and high-energy barriers in the 2DEG patterns. This new approach is promising for the development of future nano-devices operated both at low and high temperatures.
    Ultramicroscopy 06/2008; 108(10):1086-9. · 2.47 Impact Factor
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    ABSTRACT: The paper reports on a study of MOVPE growth of InMnAs dots on patterned GaAs substrates. The substrates contained [0 1 1]-oriented mesas (of trapezoidal cross-section) and ridges (of triangular cross-section) confined to facets either close to {311}A and or close to {211}A crystallographic planes. MOVPE proved to be very useful for a controlled preparation of InMnAs dots on such substrates. The analysis showed that almost no dots were grown on (100)-related strips that formed during growth by self-faceting on tops of the triangular ridges. Densities of the InMnAs dots on the {311}A-or {211}A-related facets were about 5-7 times lower compared with those on reference planar (100) substrates. On the average, the dots on the facets were larger than those formed on the reference substrates. The lateral size of the dots varied between 100 and 180 nm.
    01/2008;
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    ABSTRACT: An artificial “multigranular” YBCO thin film has been prepared by patterning a network of gridlines, emulating the current-restricting behavior of grain boundaries. This model system allowed us to investigate the magnetic effects of granularity and current percolation problem, having control on the geometry, number of grains, and ratio of inter-to-intragrain critical-current density reduction, JcGB∕JcG. The dc magnetization cycle at 5 K showed a peak shift to a positive applied magnetic field value, typically ascribed to granularity. ac measurements performed up to very high driving ac magnetic fields show that ac losses are dominated by dissipation over the whole grain boundary network, whereas the contribution of individual grains cannot be resolved. A high-resolution (<5 μm) Hall-probe imaging system has been used to visualize the evolution of the magnetization distribution with a cycled applied magnetic field (at 4.2 and 77 K), and deduce maps of the intragranular and intergranular currents by solving the inverse problem. Quantitative information about the JcGB and JcG magnetic field dependence and the spatial distribution of JcG are presented and discussed.
    Physical review. B, Condensed matter 09/2007; 76(9). · 3.66 Impact Factor
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    ABSTRACT: We have studied Si-doped n-type quantum well infrared photodetectors (QWIPs) using an Al0.28Ga0.72As/GaAs MQW heterostructure grown on patterned (001) GaAs substrate. Two patterning techniques were applied to reveal stripe patterns. Wet etching with a H3PO4-based solution using [1-10]-oriented stripe mask was used to reveal ridges confined by {111}A quasi-facets. We also prepared various mesa ridges with sidewall angle varied from 30 to 45 degree, using an additional sacrificial heterostructure based on a GaAs/AlAs system. The patterned substrates were MOVPE-overgrown to prepare nonplanar Si-doped AlGaAs/GaAs n-QWIP. Properties of non-planar multiple quantum well (MQW) heterostructures were investigated by cros-sectional transmition electron microscopy (TEM) and low temperature photoluminescence (PL). QWIP with non-planar MQW heterostructure exhibited wide absorption spectra peaked at ∼8-9 μm wavelength without additional gratings or corrugations. A relatively large asymmetry was observed in dark I-V characteristics at 77 K. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 01/2007; 4(4):1499-1502.
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    ABSTRACT: Symmetrical four-sided ∼12-μm-high pyramids with 30°-tilted sides were revealed by the etching of semi-insulating (100) GaAs substrates in 1H3PO4:×H2O2:8H2O at ∼25°C via sacrificial 〈001〉-oriented Ti/GaAs/AlAs (100/2000/100nm) etching mask patterns. The pyramids, MOCVD overgrown with InGaP/AlGaAs/GaAs heterostructure pyramids, were used as the base for magnetic field vector sensors. Each sensor consisted of three Hall probes defined on the sides of a pyramid. The device processing was realized via AZ5214-E layers deposited conformally over the pyramids by draping from water surface. While the planar reference 5×5-μm2-sized Hall probes exhibited a sensitivity of ∼930VA−1T−1 at 298K, the sensitivity of those on the 30°-tilted facets was impossible to determine because they had a resistance of ∼100kΩ at 298K. Further work is necessary to optimize the InGaP/AlGaAs/GaAs heterostructure growth and dopant incorporation on the 30°-tilted pyramidal facets.
    Microelectronics Journal 12/2006; 37:1543-1546. · 0.91 Impact Factor
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    ABSTRACT: We have studied transport of a two-dimensional electron gas through a potential barrier prepared on shallow GaAs/AlxGa 1-xAs/InGaP heterostructure by local anodic oxidation (LAO) with an AFM tip. The potential barrier height after LAO was 55 meV, and it increased to 270 meV after oxide line removal at 300 mV, at room temperature. Barriers with this height can be used for room temperature nanometre-sized structures and devices fabrication
    01/2006;
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    ABSTRACT: This work is a part of a deeper study into technologies developed for the so-called active tips for use in scanning probe microscopy. This paper show that using an AlAs facet-forming sacrificial layer and a H 3PO4, H2O2, H2O based solution, symmetric pyramidal structures with tip diameter below 35 nm can be prepared. Such pyramidal objects was used for further MOCVD overgrowth. Finally, the quality of the mesa sidewalls obtained was controlled using the SEM and AFM. The pyramids are suitable for the next processing, and various semiconductor devices can be prepared on the pyramid
    01/2006;
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    ABSTRACT: Not Available
    Advanced Semiconductor Devices and Microsystems, 2004. ASDAM 2004. The Fifth International Conference on; 02/2004
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    ABSTRACT: fabrication of advanced semiconductor structures. This problem was studied by several authors in the past [1−5 ]. Influence of growth parameters on the layer morphology prepared on various patterns was reported in these papers. Significant dependence of the morphology on the growth temperature has been observed in general. This paper also studies MOVPE growth of AlGaAs and InGaP layers on patterned GaAs substrates. The difference between this work and the data from literature lies in the shape and size of our three−dimensional patterns. A pyramid patterns with height of about 10 micrometers and various slopes of sidewalls were overgrown in our experiments. The sidewalls were prepared as non−crystallographic layers, contrary to structures published by other authors. The main goal of this work was to prepare structures with sufficiently large sidewalls. They can serve as a base for novel devices exploiting properties of two−dimensional electron gas prepared at them.
    10th European Workshop on MOVPE, 8−11 June 2003; 06/2003
  • J. Soltys, V. Cambel, J. Fedor
    Acta Physica Polonica Series a 01/2001; 103. · 0.53 Impact Factor