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1
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Monte Carlo Treatment of Non-Equilibrium Processes in n-Type InSb Crystals

100%
Ašmontas S., Raguotis R.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
929-932
EN
Numerical calculation by Monte Carlo method of the dynamic behaviour of electron ensemble in n-type InSb crystals after step-like application of electric field is presented. The results show essential influence of electron density on the energy relaxation time. The effect of electron energy cooling below equilibrium temperature in compensated n-InSb is obtained numerically for the first time, which is in agreement with experimental results.
2
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Hot-Electron Effects in High-Resistivity InSb

81%
Ašmontas S., Subačius L., Valušis G.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
717-720
EN
We report that in the presence of random potential of the conduction band hot-electron transport can exhibit some novel features, some of which can be observed in dependencies of electric conductivity, mean electron energy and noise temperature on electric field strength.
3
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A Method for Measuring the Specific Electrical Conductivity of an Anisotropically Conductive Medium

81%
Ašmontas S., Kleiza V., Kleiza J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 6
1559-1569
EN
The paper deals with the ways of finding an electrical conductivity tensor of a plane and anisotropically conductive sample. Application of the Van der Pauw method to investigate the conductivity of anisotropically conductive media makes the basis of research. Several models of distribution of the electric field potential are presented, their merits and demerits are discussed, and the necessary physical measurements are indicated. On the basis of these models, the respective calculation expressions of the specific conductivity tensor are derived and algorithms for their realization and error calculation are developed.
4
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Applicable Damage of High-T_{ rm c} YbaCuO Superconducting Tapes by Current and Laser Pulses

81%
Kiprijanovič O., Ašmontas S., Anisimovas F., Gradauskas J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
256-258
EN
Damage and irreversible damage of YBaCuO tapes with high density current after switching from superconducting to normal state are investigated. Quasi-homogeneous current distribution across the tape in superconducting state can cause perfect tape damage or irreversible damage when current is slightly above critical value. The model of the tape heating during the optically initiated switching from superconducting to normal state is proposed. Analysis of causes inducing damage shows necessity to consider 0.5T_{m} damage criterion because of strong current influence on the damage processes. Possible damage mechanisms are described and crack tips motion simultaneously with switching from superconducting to normal state is considered. Application of optically illuminated YBaCuO tapes with nanosecond duration current pulses on the base of the described mechanisms is proposed.
5
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Fast Detection of Infrared Laser Pulses on Planar Small Area GaAs/AlGaAs Heterojunction

71%
Širmulis E., Kazlauskaitė V., Gradauskas J., Sužiedėlis A., Ašmontas S.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
851-854
EN
We report the first experimental observation of fast photovoltage in small area GaAs/AlGaAs heterojunction planar detector induced by nanosecond CO_2 laser pulses. This device revealed itself as a sensitive detector of millimeter waves and as a fast IR sensor operating at room temperature. Taking into account fast response of the detector and close to linear voltage-power dependence, the results are interpreted by photoemission of hot carriers over the potential barrier of the heterojunction.
6
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Submicrometric Heavily Doped n-GaAs Structures for Microwave Detection

71%
Ašmontas S., Gradauskas J., Kozič A., Shtrikmann H., Sužiedėlis A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
147-150
EN
Strong coupling between electrons and phonons in heavily doped semiconductors impedes, in general, investigation of hot carrier phenomena in the material. Investigations of hot electron electromotive force arising in symmetrically and asymmetrically shaped structures of heavily doped n-GaAs under microwave radiation are presented in this paper. Mesas of MBE grown n-GaAs layers with neck shaped down to submicron dimensions revealed strong dependence of voltage sensitivity of the structure on the size of the neck. Slight frequency dependence of voltage sensitivity of the microwave diodes with both symmetrically and asymmetrically shaped n-n^+ junctions was observed experimentally in K_a frequency range, which coincides well with theoretical predictions.
7
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Asymmetrically Shaped Pseudomorphic Modulation Doped Structure for Microwave Detection

62%
Kozič A., Paškevič Č., Sužiedėlis A., Gradauskas J., Ašmontas S., Szerling A., Wrzesińska H.
Acta Physica Polonica A
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2006
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vol. 110
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issue 6
845-849
EN
In this paper we propose a microwave detector based on a AlGaAs/InGaAs/GaAs structure. Its operation relies on non-uniform carrier heating of the two-dimensional electron gas in the microwave electric fields which is a result of the asymmetric shape of the device fabricated on the base of pseudomorphic modulation doped AlGaAs/InGaAs/GaAs structure. The voltage sensitivity of the device at nitrogen temperature is 38 V/W for 10 GHz radiations and is higher compared to that of modulation doped AlGaAs/GaAs of the same configuration.
8
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Peculiarities of Excitonic Photoluminescence in Si δ-Doped GaAs Structures

62%
Nargelienė V., Ašmontas S., Čerškus A., Gradauskas J., Kundrotas J., Sužiedėlis A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
177-179
EN
We present investigation of photoluminescence properties of Si δ-doped GaAs structures at different temperatures and various laser excitation intensities. Strong excitonic emission was observed in the δ-doped structures. The photoluminescence in the infrared region, below excitonic emission, originates from a non-phonon free electron-acceptor e-A transitions and longitudinal optical phonon sidebands of e-A transitions. Possible mechanisms for recombination of photocarriers are discussed, with a particular focus on an enhanced excitonic photoluminescence emission in comparison with that from intrinsic GaAs layers of the same structures.
9
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Magnetoresistive Properties of Manganite-Based Heterojunctions

62%
Devenson J., Vengalis B., Lisauskas V., Oginskis A., Anisimovas F., Ašmontas S.
Acta Physica Polonica A
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2009
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vol. 115
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issue 6
1130-1132
EN
Hole-doped La_{2/3}Ba_{1/3}MnO_{3} (LBaMO), La_{2/3}Ca_{1/3}MnO_{3} (LCaMO) and La_{2/3}Ce_{1/3}MnO_{3} (LCeMO) thin films were grown heteroepitaxially on 0.1 wt.% Nb-doped SrTiO_{3}(100) (STON) substrates by magnetron sputtering. The prepared LBaMO/STON, LCaMO/STON, LCeMO/STON heterostructures demonstrated nonlinear rectifying current-voltage characteristics. Negative magnetorestance values have been indicated at low bias, meanwhile bias-dependent magnetoresistance has been measured at positive bias voltage values U > U_d where U_d is the interfacial potential, corresponding to a steep current increase at a forward bias.
10
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Peculiarities of High Power Infrared Detection on Narrow-Gap Semiconductor p-n Junctions

62%
Gradauskas J., Širmulis E., Ašmontas S., Sužiedėlis A., Dashevsky Z., Kasiyan V.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
237-240
EN
We report on experimental results of photosignal investigation in HgCdTe, InSb and PbTe semiconductor p-n junctions under the action of an intense pulsed CO_2 laser. The influence of laser power, external bias voltage as well as the diode temperature on the photosignal formation has been studied. We show that under certain conditions both classical photovoltaic and hot carrier phenomena may act simultaneously within a junction thus strongly impacting on responsivity and speed of operation of the device. The drawn conclusions may be of great importance for the development of high power optoelectronic devices.
11
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Studies of Response of Metal - Porous Silicon Structures to Microwave Radiation

62%
Stupakova J., Ašmontas S., Gradauskas J., Zagadskij V., Shatkovskis E., Sužiedėlis A.
Acta Physica Polonica A
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2006
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vol. 110
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issue 6
817-822
EN
Structures containing layers of porous silicon with two metal contacts are investigated. Porous silicon is manufactured by anodizing p-type crystalline silicon plates of resistivity of 0.4 Ω cm. Contacts for the samples are made by additional boron doping of the surface and by thermal evaporation of aluminium. Resistance and current-voltage characteristics are investigated. Response of the porous silicon layer containing structures under action of pulsed microwave radiation was investigated for the first time. The origin of the response is discussed.
12
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Reversible Resistive Switching in Electrically Nonhomogeneous La_{0.67}Ca_{0.33}MnO_3 Thin Films by Short Electrical Pulses

62%
Lučun A., Kiprijanovič O., Ašmontas S., Anisimovas F., Maneikis A., Sužied.lis A., Vengalis B.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
1059-1062
EN
Resistance changes in thin electrically nonhomogeneous La_{0.67}Ca_{0.33}MnO_3 films were investigated using electrical pulses of nanosecond duration in the 80-300 K temperature range. Two types of reversible switching to higher resistive states with different starting temperature induced by series of the positive pulses were observed. Possible mechanisms of the resistance switching by short electrical pulses in the vicinity of T_m and at 80-90 K are discussed.
13
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Hot Electron Effect in Degenerate Semiconductor Tunnel Junction

62%
Ašmontas S., Gradauskas J., Petkun V., Seliuta D., Sužiedėlis A., Urbelis A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
198-202
EN
We report on the results of experimental study of free carrier heating in degenerate GaAs tunnel p-n diodes when the carriers are excited by pulsed microwave radiation. Free carrier heating is responsible for the electromotive force in the diode. The magnitude of the electromotive force linearly depends on pulsed microwave power and increases with the decrease in semiconductor lattice temperature. It is almost independent of the pulsed microwave frequency and of p-n junction plane orientation in respect to electric field direction. In the tunnelling regime the dark current in the diode is reduced, however, at high enough forward bias the diffusive current is stimulated due to hot carrier phenomenon.
14
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Enhancement of the Excitonic Photoluminescence in n^{+}/i-GaAs by Controlling the Thickness and Impurity Concentration of the n^{+} Layer

52%
Čerškus A., Nargelienė V., Kundrotas J., Sužiedėlis A., Ašmontas S., Gradauskas J., Johannessen A., Johannessen E.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
154-157
EN
This communication presents the photoluminescence spectra of molecular beam epitaxially grown GaAs structures made from a 500 nm thick layer of intrinsic conductivity capped with a silicon doped layer with a film thickness ranging from 10 to 100 nm. Two different doping concentrations of the cap layer, N_{Si} = 10^{17} cm^{-3} and N_{Si} = 10^{18} cm^{-3}, was considered. The results showed the excitonic line of i-GaAs layer enhancement. The intensity of excitonic line was about 160 times higher for the homojunction compared to the intrinsic conductivity epitaxial layer at liquid helium temperature. Possible mechanisms of the observed intensity enhancement in the n^{+}/i-GaAs homojunction are discussed.
15
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Phase Separation and Microwave Response of Epitaxial and Polycrystalline Manganite Films

52%
Ašmontas S., Abrutis A., Gradauskas J., Lučun A., Oginskis A., Plaušinaitienė V., Sužiedėlis A., Vengalis B.
Acta Physica Polonica A
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2004
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vol. 105
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issue 1-2
141-147
EN
The resistance, magnetoresistance, and resistance response under microwave irradiation (f=10 and 35 GHz) were measured for epitaxial and polycrystalline La_{0.67}Ca_{0.33}MnO_3 and La_{0.67}Sr_{0.33}MnO_3 thin films in the temperature range 78÷300 K. The microwave induced resistance increase observed for the epitaxial films in a narrow temperature range below the ferromagnetic to paramagnetic transition temperature T_c certifies coexistence of low resistance (ferromagnetic) and high resistance (paramagnetic) regions in the manganites. Resistance of polycrystalline films decreased under microwave irradiation in a wide temperature range below T_c. The effect was explained in terms of microwave assisted hopping of carriers in high resistance regions formed at grain boundaries of the polycrystalline films.
16
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Mesoscopic Structures for Microwave-THz Detection

52%
Sužied.elis A., Ašmontas S., Požela J., Kundrotas J., Širmulis E., Gradauskas J., Kozič A., Kazlauskaité V., Anbinderis T.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
803-809
EN
Properties of microwave detectors of various design on the base of MBE grown GaAs and AlGaAs structures are discussed in this paper: simple asymmetrically shaped structures with heavily doped GaAs and AlGaAs layers of nanometric thickness as well as diodes with two-dimensional electron gas layers. Novel models of the detectors with partially gated two-dimensional electron gas layer as well as with small area GaAs/AlGaAs heterojuction are discussed to demonstrate different ways to increase the voltage sensitivity of the detectors of electromagnetic radiation in GHz-THz frequency range.
17
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Electroresistance of Electrically Nonhomogeneous La_{0.67}Ca_{0.33}MnO_3/MgO Thin Films

52%
Kiprijanovič O., Lučun A., Ašmontas S., Anisimovas F., Butkutė R., Maneikis A., Sužiedėlis A., Vengalis B.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
141-146
EN
Current and electrical field-induced electroresistive effects were investigated for La_{0.67}Ca_{0.33}MnO_3/MgO thin films demonstrating nanosized electrical inhomogeneities. Two different models based on enhanced conductivity of intergrain boundaries by injecting spin-polarized carriers from ferromagnetic grains and electrical field-enhanced hopping of carriers in high resistance intergrain media were carried out to explain nonlinear electrical properties of the films.
18
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Magnetoresistance of Polycrystalline La_{0.7}Ca_{0.3}MnO_3 Films in a Microwave Magnetic Field

52%
Lučun A., Butkutė R., Maneikis A., Kiprijanovič O., Anisimovas F., Gradauskas J., Sužiedėlis A., Vengalis B., Kancleris Ž., Ašmontas S.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
147-152
EN
We present new experimental evidence indicating the importance of magnetic field component of microwave field (f=9.4 GHz) for magnetoresistive properties of polycrystalline La_{0.7}Ca_{0.3}MnO_3 films. The microwave measurements revealed a different character of the temperature-dependent electrical resistance of polycrystalline La_{0.7}Ca_{0.3}MnO_3 films placed in the centre (maximal amplitude of H_{10} wave vector) and at a narrow wall of the wave-guide (reduced H_{10} amplitude). Theoretical estimations of the influence of substrate onto distribution of microwave electric and magnetic fields in the waveguide were performed using the finite-difference time-domain method.
19
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Experimental Study of Optical Transitions in Be-Doped GaAs/AlAs Multiple Quantum Wells

52%
Kundrotas J., Čerškus A., Ašmontas S., Valušis G., Sherliker B., Halsall M., Harrison P., Steer M.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
245-249
EN
We present a photoluminescence study of optical transitions in Be acceptor-doped GaAs/AlAs multiple quantum wells at room and liquid nitrogen temperatures. We investigate excitonic spectra and reveal acceptor-impurity induced effects in multiple quantum wells having different width.
20
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High Power Microwave Detection in Asymmetrically Shaped n-Al_xGa_{1-x}As Structures

52%
Ašmontas S., Čerškus A., Gradauskas J., Kundrotas J., Lučun A., Petkun V., Sužiedėlis A., Šilėnas A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
315-318
EN
Investigations of detection of high power microwaves in planar asymmetrically shaped microwave diodes on the basis of Al_xGa_{1-x}As ternary semiconductors with various AlAs mole fraction are presented. The principle of operation of the microwave diodes is based on carrier heating phenomena in asymmetrically shaped homogeneous semiconductor structure due to different distribution of the electric field strength along the sample. Experimental results of microwave detection on the barrier-less asymmetrically shaped diodes are presented paying special attention to the homogeneity of Al_xGa_{1-x}As which was monitored by photoluminescence technique.
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