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1
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Fast Detection of Infrared Laser Pulses on Planar Small Area GaAs/AlGaAs Heterojunction

100%
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.
2
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Submicrometric Heavily Doped n-GaAs Structures for Microwave Detection

100%
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.
3
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Charge Carrier Heating Effect in Porous Silicon Structures Investigated by Microwaves

100%
Gradauskas J., Šatkovskis E., Česnys A., Stupakova J., Sužiedėlis A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
993-996
EN
Diode-like samples, containing porous silicon structures, were investigated by microwave radiation pulses. The resistance of the samples and electromotive force arising over the samples placed in a section of waveguide was measured. Reduction of resistance of the samples was observed with increase in microwave power. More complicated shape of the electromotive force dependence on pulse power was found. It is shown that both effects could be explained by models based on a concept of carrier heating by microwave radiation.
4
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Enhanced Electron Saturated Drift Velocity in AlGaAs/GaAs/AlGaAs Heterostructures

100%
Požela J., Požela K., Sužiedėlis A., Jucienė V., Petkun V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
989-992
EN
A new approach for reduction of scattering rate of electrons by polar optical phonons in the double barrier heterojunction quantum well is proposed. This approach is based on the phonon localization in narrow phonon wells. The enhancement of the electron saturated drift velocity in the Al_{0.2}Ga_{0.8}As/GaAs/Al_{0.2}Ga_{0.8}As high electron mobility transistor channel is envisaged theoretically and observed experimentally. The drift velocity in the channel in high electric fields (E >10 kV/cm) exceeded the maximal drift velocity in bulk GaAs (v_{max}=10^7 cm/s) and achieved the value of 4×10^7 cm/s.
5
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Asymmetrically Shaped Pseudomorphic Modulation Doped Structure for Microwave Detection

86%
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.
6
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Peculiarities of Excitonic Photoluminescence in Si δ-Doped GaAs Structures

86%
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.
7
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Peculiarities of High Power Infrared Detection on Narrow-Gap Semiconductor p-n Junctions

86%
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.
8
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Studies of Response of Metal - Porous Silicon Structures to Microwave Radiation

86%
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.
9
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Hot Electron Effect in Degenerate Semiconductor Tunnel Junction

86%
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.
10
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Enhancement of the Excitonic Photoluminescence in n^{+}/i-GaAs by Controlling the Thickness and Impurity Concentration of the n^{+} Layer

73%
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.
11
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Phase Separation and Microwave Response of Epitaxial and Polycrystalline Manganite Films

73%
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.
12
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Electroresistance of Electrically Nonhomogeneous La_{0.67}Ca_{0.33}MnO_3/MgO Thin Films

73%
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.
13
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Magnetoresistance of Polycrystalline La_{0.7}Ca_{0.3}MnO_3 Films in a Microwave Magnetic Field

73%
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.
14
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Frequency Dependence of Electrical Response of Polycrystalline LCMO Thin Films

73%
Ašmontas S., Anisimovas F., Balevičius S., Cimmperman P., Gradauskas J., Lučun A., Stankevič V., Sužiedėlis A., Vengalis B., Žurauskienė N.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
193-197
EN
Influence of strong electric field in wide frequency range (from DC to 35 GHz) on electrical resistance of thin La_{0.67}Ca_{0.33}MnO_3 polycrystalline manganite films was investigated in the range of (78÷300) K. Different behavior of resistance change vs. temperature was observed when pulsed DC electric field and microwaves were applied to the films. When pulsed DC electric field is applied the electric-field-induced resistance change ("electroresistance") of manganite film depended nearly monotonically on temperature. However, in microwave electric fields a non-monotonic character of the electroresistance temperature dependence was observed. The dependence of the electroresistance on quality of manganite films was observed in case of microwaves. The experimental findings are explained assuming different electrical current mechanisms in case of DC and microwave fields. The applied voltage drops mainly across the grains of polycrystalline film due to a presence of displacement currents in case of microwaves, whereas in DC case the voltage drop is across the grain boundaries.
15
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High Power Microwave Detection in Asymmetrically Shaped n-Al_xGa_{1-x}As Structures

73%
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.
16
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Electron Transport in Modulation-Doped InAlAs/InGaAs/InAlAs Heterostructures in High Electric Fields

59%
Požela K., Požela J., Jucienė V., Vasil'evskii I., Galiev G., Klimov E., Sužiedėlis A., Žurauskienė N., Stankevič V., Keršulis S., Paškevič Č.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
170-172
EN
The following peculiarities of electron transport in In_{0.53}Ga_{0.47}As/In_{0.52}Al_{0.48}As quantum wells with δ-Si-doped In_{0.52}Al_{0.48}As barriers at high electric fields are discovered: (1) an enhancement of electron mobility by inserting the InAs phonon wall into the In_{0.53}Ga_{0.47}As/In_{0.52}Al_{0.48}As quantum well, as well as increasing the InAs content in the modulation-doped In_{0.8}Ga_{0.2}As/In_{0.7}Al_{0.3}As heterostructure; (2) a large decrease in electron mobility and a change of electron density with increasing electric field in the range of 1-4 kV/cm; (3) a magnetic field dependence of the threshold electric field for intervalley scattering of electrons; and (4) microwave current oscillations in high electric fields.
17
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Influence of Magnetic Field on Detection Properties of Planar Microwave Diodes

59%
Sužiedėlis A., Ašmontas S., Požela J., Gradauskas J., Nargelienė V., Paškevič Č., Derkach V., Golovashchenko R., Goroshko E., Korzh V., Anbinderis T.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
218-221
EN
The results of experimental investigation of detection properties of the planar microwave diodes of various configuration on DC magnetic field are presented in this paper. The detection of microwave radiation was measured at 51 GHz, 72 GHz and 144 GHz frequencies. The magnetic field was applied in plane and perpendicularly to the plane of the diodes. The experiment was performed at room temperature. Dependence of the detected voltage of the diodes on the magnetic field had asymmetric character with respect to the polarity of the magnetic field. This fact allowed us to suspect the magnetic rectification influencing the detected voltage. Therefore, average value of the detected voltage with respect to the polarity of the applied magnetic field gives its dependence on the applied magnetic field.
18
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Broad Band THz Sensing by 2DEG Bow-Tie-Type Diodes

59%
Valušis G., Seliuta D., Tamošiūnas V., Širmulis E., Balakauskas S., Gradauskas J., Sužiedėlis A., Ašmontas S., Anbinderis T., Narkūnas A., Papsujeva I., Lisauskas A., Roskos H., Köhler K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
184-187
EN
We suggest a novel approach to detect broad band, 0.078-2.52 THz, electromagnetic radiation at room temperature using an asymmetrically-shaped bow-tie diode based on a modulation-doped GaAs/AlGaAs structure. We show that the voltage sensitivity in the range from 0.078 THz up to 0.8 THz has a plateau and its value is within 0.3-0.5 V/W. We consider the bow-tie diode design to increase the sensitivity of the device.
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