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1
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Physics of THz Field-Effect Transistors

100%
Łusakowski J.
Acta Physica Polonica A
|
2011
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vol. 119
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issue 2
114-116
EN
Field-effect transistors are nowadays considered as possible elements of THz detection and emission systems. Their THz performance is governed by excitations of two-dimensional plasma in the transistor channel. The paper discusses peculiarities of the photon-plasmon coupling mechanism in field-effect transistors and puts it in the perspective of classical investigation of plasma excitations in two-dimensional systems.
2
Content available remote

Nonlinear Coupling of Oscillatory Modes in Current Flow in Semi-Insulating GaAs

64%
Karpińska K., Łusakowski J.
Acta Physica Polonica A
|
1991
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vol. 80
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issue 3
425-428
EN
Spontaneous current oscillations in semi-insulating (SI) GaAs sample caused by high electric field domains nucleation were perturbed by modulated illumination. Coupling between domain and photocurrent oscillations leads to quasiperiodic and frequency-locked behaviour. The observed Arnol'd tongues structure follows the Farey tree ordering and agrees with predictions of the circle map theory. We also suggest a possible mechanism responsible for the coupling of the modes.
3
Content available remote

Surface Metallic Pattern for Enhancement of a THz Field in a Two-Dimensional Electron Plasma

64%
Tarkowski T., Łusakowski J.
Acta Physica Polonica A
|
2017
|
vol. 132
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issue 2
332-334
EN
A metamaterial in the form of a periodic lattice of split-ring resonators on a GaAs/AlGaAs heterostructure was numerically studied at terahertz frequencies. A finite-difference time-domain algorithm was applied to calculate distribution of the electromagnetic field in the layer positioned at 100 nm below the heterostructure surface where a two-dimensional electron gas typically resides in real structures. The results allowed to determine the resonant frequencies of the metamaterial as well as an enhancement factor of the electric field as a function of the period of the metamaterial's lattice.
4
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Current-Voltage Characteristic of Semi-Insulating GaAs, with Trap-Filling Effect

64%
Karpińska K., Łusakowski J.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 2-3
281-285
EN
A detailed investigation of current-voltage (I- V)characteristics of semi-insulating GaAs sample was performed in the vicinity of room temperature. The sample with 300 K resistivity of 2 x 10^{7} Ω cm was supplied with guard-ring electrodes which allowed the elimination of surface currents. The observed characteristics started with an ohmic part which was followed by a superlinear current on voltage dependence. At a threshold voltage V_{t}h which corresponds to the electric field of about 2 kV/cm the current increased abruptly by a few orders of magnitude. The value of V_{t}h increased with the temperature. It is proposed that the observed shape of the I-V curve is caused by the filling of the EL2 level with injected electrons heated by the electric field.
5
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Fractal Dimensions from Chaotic Oscillations in Semi-Insulating GaAs

64%
Zduniak A., Łusakowski J.
Acta Physica Polonica A
|
1993
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vol. 84
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issue 3
575-578
EN
Relaxation and domain current oscillations in undoped semi-insulating GaAs were observed at room temperature for a broad range of voltage applied to a sample. The oscillations were characterized by a reconstruction of an attractor of the system. An analysis of the attractor helped to discriminate between the two likes of oscillations. A transition from one like of oscillations to the other was connected with a chaotization of the current. A chaotic state of the system was analyzed by calculations of fractal dimensions D_{q} for -0.6 < g < 40 and the f(α) function.
6
Content available remote

Influence of Impact Ionization of Shallow Donors on Luminescence in GaAs

64%
Wysmołek A., Łusakowski J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
261-264
EN
Luminescence spectra of n-type molecular beam epitaxial layer and semi-insulating liquid encapsulated Czochralski grown bulk GaAs were mea­sured at liquid helium temperature for zero electric field and for fields which caused impact ionization of shallow donors. Application of the electric field caused a decrease in the luminescence intensity and a broadening of all ob­served structures. It was found that the electric field changed the lumines­cence spectrum of the n-type material in a different way than it did in the case of the semi-insulating one. For the n-type sample, an intensity of exci­tonic lines decreased much more than that of donor-acceptor lines when the electric field grew. A contrary was observed for the semi-insulating sample. An explanation of the result is proposed which takes into account an in­fluence of ionised impurity scattering and localization in fluctuations of the electrostatic potential on the luminescence process.
7
Content available remote

Autocorrelation Function and Mutual Information from Short Experimental Time Series

64%
Zduniak A., Łusakowski J.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 1
257-260
EN
A nonlinear dynamics of self-generated current oscillations in semi-insu­lating GaAs was studied by the reconstruction of an attractor from a short (14500 points) time series. Two methods of choosing of a time constant (τ) for this reconstruction are compared. One of them assumes τ to be an argu­ment of the first zero of the autocorrelation function and the other takes τ as an argument of the first minimum of the mutual information. It is shown that for periodic oscillations both methods are equivalent, but for chaotic ones only the mutual information gives a time constant which does not depend on a time series used for calculations.
8
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Electron Temperature in Semi-Insulating GaAs for Low Electric Fields

52%
Zduniak A., Łusakowski J., Nowak G.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
777-780
EN
Heating of electrons by electric fields smaller than that required for generation of domain oscillations was investigated in samples of EL2-rich semi-insulating GaAs. Current-voltage characteristics were measured as a function of temperature between 268 K and 330 K. They exhibit a sublinear shape which is interpreted as a result of an enhanced electron capture on the EL2. The capture rate and the electron temperature as a function of the electric field was determined. A fitting procedure gave the value of electron capture cross-section on the EL2 to be 2.7 × 10^{-13} cm^{2} which agrees with literature data.
9
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Magnetic Field Induced Localization in Semiinsulating GaAs

52%
Łusakowski J., Merten R., Grynberg M.
Acta Physica Polonica A
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1992
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vol. 82
|
issue 4
551-560
EN
Conductivity experiments were carried out on samples of semiinsulating GaAs at liquid helium temperature in magnetic field up to 6 T. During the measurements the samples were persistently illuminated with infrared light which allowed to populate with electrons a part of shallow donor and conduction band states. Current-voltage characteristics showed an abrupt jump of the current at a threshold electric field which is interpreted as a result of impact ionization of electrons bound on shallow donors and in the tail of the bottom of the conduction band. The jump of the current decreases as the magnetic field increases and disappears for a sufficiently high magnetic field B_{0}. The value of B_{0} grows with growing light intensity. These results are explained by magnetic-field induced localization of electrons on long-range fluctuations of the electrostatic potential. The localization transition was confirmed by the current dependence on temperature measured at different magnetic fields. A peak on these curves was observed. Its position coincides with the temperature above which impact ionization is not observed. A possible mechanism explaining appearance of the peak is presented.
10
Content available remote

Response of Indium Antimonide at Sub-Terahertz and Terahertz Frequencies

52%
Yavorskiy D., Karpierz K., Grynberg M., Łusakowski J.
Acta Physica Polonica A
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2017
|
vol. 132
|
issue 2
338-339
EN
Responsivity of a bulk InSb detector at liquid helium temperature was studied in the frequency range 0.1 THz
11
Content available remote

Conductivity of Optically Excited Electrons in GaAs in Quantizing Magnetic Fields

52%
Łusakowski J., Grynberg M., Huant S.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 2
482-486
EN
Magnetoconductivity (σ) measurements on an n-type molecular beam epitaxy grown epitaxial layer and on a bulk liquid encapsulated Czochralski grown undoped semi-insulating GaAs samples were performed for magnetic fields (B) up to 21 T at 4.2 K. To enable current measurements in a wide range of B both samples were permanently illuminated with a band-to-band light. It is shown that for sufficiently high magnetic fields σ(B) dependence is the same for both materials. This result underlines a role of scattering by long-range fluctuations of the electrostatic potential in high-quality n-GaAs in quantizing magnetic fields.
12
Content available remote

Exciton Binding Energy and Oscillator Strength in a Shallow Quantum Well in an External Magnetic Field

52%
Zięba P., Piętka B., Łusakowski J., Tralle I.
Acta Physica Polonica A
|
2015
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vol. 128
|
issue 2
237-239
EN
We discuss the influence of an external magnetic field on the exciton energy and the exciton oscillator strength in the shallow quantum wells. We include into consideration the Coulomb attraction between electron and hole, which is rarely taken into account. We self-consistently solve the Schrödinger equation to compare the obtained results with the experimental values.
13
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Photoluminescence of CdTe/CdMgTe Double Quantum Wells with a Two-Dimensional Electron Gas

46%
Deresz M., Wiater M., Karczewski G., Wojtowicz T., Łusakowski J.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 2
390-392
EN
Magnetophotoluminescence measurements at liquid helium temperatures were carried out on asymmetric double quantum wells based on CdTe/CdMgTe heterostructures. Due to doping with shallow iodine donors, a two-dimensional electron gas was present in the quantum wells. The samples studied differed with the quantum well widths and doping level. We show a resemblance of the luminescence to results obtained on single quantum wells which suggests that in samples studied the quantum wells are not strongly coupled.
14
Content available remote

Local Electric In-Plane Potential Fluctuations in the CdTe/CdMgTe Based Multiple Quantum Wells

46%
Nogajewski K., Karpierz K., Łusakowski J., Grynberg M., Kossut J.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1259-1265
EN
Unusual features in the magnetophotoconductivity spectra registered under far infrared illumination of the CdTe/CdMgTe based multiple quantum wells, uniformly n-doped are presented. It is shown that each spectrum exhibits one or two peaks of non-symmetrical shape, with position of their maxima dependent on the voltage applied to the sample. The peaks, observed in the configuration of the crossed electric and magnetic fields, are strongly shifted by a relatively weak in-plane electric field - of the order of 10-50 V/cm. Two different approaches to explain the observed influence are presented. Both are based on a two-step process leading to the photoconductivity signal. The first approach assumes that only the process of photon absorption is influenced by the external fields, the second one assumes that only the process of phonon assisted electron transfer from the excited donor state into the conduction band is influenced by the external fields.
15
Content available remote

Sub-Terahertz Emission from Field-Effect Transistors

46%
Yavorskiy D., Karpierz K., Kopyt P., Grynberg M., Łusakowski J.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 2
335-337
EN
Several commercially available field-effect GaInAs-based transistors were studied as emitters of electromagnetic radiation. The emitters were tested either at room or at liquid helium temperature. To spectrally analyse emitted radiation, we applied three different experimental techniques: a spectrum analyser with antennas and mixers, a Michelson interferometer and a magnetic-field-tunable InSb detector. We show that the emission consists of a fundamental frequency of 11.5 GHz and its multiple harmonics spanning the emission band up to about 400 GHz. Analysis of the results allows us to suggest that the emission is caused by a Gunn effect and a high harmonics content is related to a pulse-like time dependence of the current.
16
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Content available

Magnetoconductivity of GaAs Transistors as Detectors of THz Radiation

46%
Łusakowski J., Knap W., Kamińska E., Piotrowska A., Gavrilenko V.
Acta Physica Polonica A
|
2003
|
vol. 103
|
issue 6
545-551
EN
Magnetotransport characterisation of field effect transistors processed on GaAs/GaAlAs heterostructure was done at 4.2 K for magnetic fields (B) up to 7 T. Three field effect transistors were processed on a single dice and differed by the length (L) of the gate. Electron mobility (μ) in field effect transistors was estimated from dependence of transistor's conductivity vs. B. The results show a decrease inμ with decreasing L that suggests that scattering by edges of the gated part of a transistor limits the electron mobility. Quality factor (Q) of transistors as resonant detectors of THz radiation was calculated. A high value of Q shows that such field effect transistors with sub-micron L are promising devices that can operate at THz frequencies.
17
Content available remote

Optical Γ₆ → Γ₈ Free-to-Bound Transitions in Acceptor δ-Doped Single Heterostructure - Theoretical Analysis

46%
Buczko R., Łusakowski J., Friedland K., Hey R., Ploog K.
Acta Physica Polonica A
|
2008
|
vol. 114
|
issue 5
1079-1083
EN
A theoretical analysis was carried out of an optical transition observed in high-quality GaAs/AlGaAs heterostructures δ-doped with shallow acceptors. The transition involves a 2D electron and a 3D acceptor-localized hole. The wave functions of a bulk Be acceptor were calculated within the spherical model with both the s-like and d-like parts of the envelope taken into account. The electron envelope wave functions resulted from self-consistent calculations of the electrostatic potential and were dependent on the 2D electron concentration, n_s. We show that: (i) including the d-like part of the acceptor envelope relaxes the selection rules of free-to-bound transitions at k=0;(ii) in the magnetic field, the selection rules depend on the number of the electron Landau level;(iii) the ratio of the intensity of the strongest transitions in both circular polarizations is essentially different from 3:1, and strongly depends on n_s. These results show that a description that neglects the d-like part of the acceptor envelope is both qualitatively and quantitatively unjustified.
18
Content available remote

Resonant Plasmon Response of a Periodically Modulated Two-Dimensional Electron Gas

46%
Sznajder P., Piętka B., Szczytko J., Łusakowski J., Bardyszewski W.
Acta Physica Polonica A
|
2012
|
vol. 122
|
issue 6
1090-1092
EN
We report the theoretical study of the optical response of a periodically modulated two-dimensional electron gas. The density of states is calculated within the first order of the perturbation theory and the effects of the short-range disorder are explained and discussed. We demonstrate that the magnetic field values corresponding to the characteristic narrowing of the density of states width are given by the zeros of the subsequent Laguerre polynomials. The observed increase of the density of states at the edges are interpreted as van Hove singularities. The broadening effects are shown to modify and smear out the observed effects with increasing temperature above 2 K. The plasmon dispersion relation is discussed in terms of the random phase approximation. Small changes in plasmon dispersion relation related to the periodic modulation were predicted.
19
Publication available in full text mode
Content available

Terahertz Generation and Detection by Plasma Waves in Nanometer Gate High Electron Mobility Transistors

46%
Knap W., Łusakowski J., Teppe F., Dyakonova N., Meziani Y.
|
EN
The high electron mobility transistors can act as a resonator cavity for the plasma waves that can reach THz frequencies for a nanometer size devices. As was predicted by Dyakonov and Shur in 1993, the steady state of the current flow in a gated 2D electron gas can become unstable leading to the emission of an electromagnetic radiation at the plasma wave frequencies. The theory predicted also that the plasma waves can be used for resonant detection of THz electromagnetic radiation. In the present paper we review our recent experiments on THz emission and detection performed on high electron mobility transistors based on different semiconductor structures: InGaAs/GaAlAs, GaAs/GaAlAs, and Si.
20
Content available remote

Non-Ohmic Conductivity of High Resistivity CdTe

39%
Łusakowski J., Szczytkowski J., Szadkowski K., Kamińska E., Piotrowska A., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
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1995
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vol. 88
|
issue 4
803-806
EN
Conductivity measurements were carried out at room temperature on samples of nominally undoped Bridgman, bulk crystals and MBE-grown lay­ers of CdTe. The samples were equipped with indium contacts which made it possible to determine the voltage distribution along the path of the cur­rent flow. The results show that for both types of CdTe almost all of the applied voltage drops in the vicinity of the positively biased contact. The resistance of the samples was shown not to depend on the distance between the pads. The results agree with predictions of model of current injection into semiconductors with deep traps.
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