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  1. 31 Acta Physica Polonica A

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  1. 5 Liberis J.

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  3. 4 Požela J.

  4. 4 Sužiedėlis A.

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1
Content available remote

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
|
2008
|
vol. 113
|
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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Resonant Transmission in Effective-Mass "Double-Barrier" System

100%
Riesz F.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
505-507
EN
The transmission characteristic of barrierless ABABA multilayer sys­tem, where A and B are materials with differing effective masses, is ana­lyzed. The system shows resonant transmission similarly to a conventional double-barrier system, but shows unique features: unity transmission at zero energy, a more structured nature of the transmission versus energy curve and a non-decreasing peak-to-valley ratio with increasing energy.
3
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In-Plane/Tilted Magnetic-Field-Dependent Conductance of 2D Electron Systems in Asymmetric Double Quantum Wells

100%
Smrčka L., Vašek P., Jungwirth T., Makarovskii O. N., Cukr M., Jansen L.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 5
981-984
EN
The resistance in an asymmetric double-well structure was measured as a function of magnetic fields oriented almost parallel to the plane of the electron layer. It was shown that the shape of the magnetoresistance curves is close to the in-plane magnetic-field-dependent density of states which we obtained by self-consistent numerical calculation. The novel feature is the negative magnetoresistance observed at low magnetic fields.
4
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Influence of Screening and Electric Field on Exciton Binding Energy in Asymmetric Double Quantum Well

100%
Olejníková B.
Acta Physica Polonica A
|
1995
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vol. 87
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issue 2
353-356
EN
The influence of screening by confined free electrons on the exciton binding energy in the asymmetric double quantum well is calculated for var­ious values of applied electric field perpendicular to the layer plane. The dependence of the exciton binding energy on carrier concentration is found to be stronger for lower than for higher fields. The drop of field-dependent exciton energy is less remarkable at higher densities of free electrons. Calcu­lations were performed at 10 and 300 K, and up to densities of 10^{14} m^{-2} and 7 × 10^{14} m^{-2}, respectively.
5
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Charge Carrier Transport in Artificially Structured Two-Dimensional Semiconductor Systems

100%
Walukiewicz W.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 1
35-46
EN
General aspects of the electronic transport in two-dimensional and quasi-three-dimensional semiconductor systems are discussed. Contributions of different scattering processes to the total electron and hole mobilities in various types of modulation doped heterostructures are calculated. It is shown that in a wide temperature range phonon scattering is the principal scattering mechanism limiting electron and hole mobilities in high quality AlGaAs/GaAs modulation doped heterostructures. Scattering from rough walls in wide parabolic wells is briefly reviewed.
6
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Hot-Phonon Decided Carrier Velocity in AlInN/GaN Based Two-Dimensional Channels

100%
Ardaravičius L., Kiprijanovič O., Liberis J.
Acta Physica Polonica A
|
2011
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vol. 119
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issue 2
231-233
EN
Nanosecond-pulsed measurements of hot-electron transport were performed for a nominally undoped two-dimensional channel confined in a slightly strained Al_{0.8}In_{0.2}N/AlN/GaN and nearly lattice matched Al_{0.84}In_{0.16}N/AlN/GaN heterostructures at room temperature. No current saturation is reached because we minimized the effect of the Joule heating. The electron drift velocity is deduced under assumption of uniform electric field and field-independent electron density. The estimated drift velocity ≈ 1.5 × 10^7 cm/s at 140 kV/cm bodes well with the value of hot-phonon lifetime exceeding 0.1 ps.
7
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Spin-Orbit-Coupling, Electric-Field and Free-Carrier-Screening Effects on Valence Band Structure of Strained Coupled Quantum Wells

100%
Olejníková B.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
940-944
EN
We have calculated the structure of the valence bands and its dependence on the electric field and the density of free carriers in a lattice mismatched single and double quantum well. Our calculation is based on simultaneous solving of the effective mass equation for the envelope functions and Poisson's equation. The 6×6 Luttinger-Kohn Hamiltonian is diagonalized into two 3×3 blocks by a unitary transformation. We have shown how including the coupling between spin-orbit split-off band and light- and heavy-hole bands influences the shape of the valence bands. Further it has been found that at high densities of the free carriers and at non-zero electric field, the free-carrier screening affects the valence band structure and wave functions. This effect is considerably pronounced in double quantum well because of large spreading of the quantum states. The studying of the above effects is useful for band-structure engineering.
8
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Bands, Bonds, and Polarizations in Nitrides - from Electronic Orbitals to Electronic Devices

100%
Majewski J., Zandler G., Vogl P.
Acta Physica Polonica A
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2001
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vol. 100
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issue 2
249-260
EN
A key property of the nitrides is the fact that they possess large spontaneous and piezoelectric polarization fields that allow a significant tailoring of the carrier dynamics and optical properties of nitride devices. In this paper, based on first-principles calculations of structural and electronic properties of bulk nitrides and their heterostructure, we investigate the potential of this novel material class for modern device applications by performing self-consistent Monte Carlo simulations. Our studies reveal that the nitride based electronic devices have characteristics that predispose them for high power and high frequency applications. We demonstrate also that transistor characteristics are favorably influenced by the internal polarization induced electric fields.
9
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Electrical and Optical Characteristics of n-GaSb/n-GaIn_{0.24}AsSb/p-GaAl_{0.34}AsSb Heterostructure Photodiode

80%
Ahmetoglu M., Kucur B., Andreev I., Kunitsyna E., Mikhailova M., Yakovlev Y.
Acta Physica Polonica A
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2015
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vol. 127
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issue 4
1007-1009
EN
In the present paper, electrical and optical properties of n-GaSb/n-GaIn_{0.24}AsSb/p-GaAl_{0.34}AsSb double heterostructure (DH) with a diameter of 0.3 mm are reported. The current-voltage (I-V) characteristics of the structure were investigated at several temperatures in both, dark and under the illumination conditions. The effect of illumination was studied at different intensity values. Short circuit current and open circuit voltage as a function of intensity of incident light in photovoltaic mode are investigated.
10
Publication available in full text mode
Content available

High-Frequency Noise Sources in Quantum Wells

80%
Ardaravičius L., Liberis J., Matulionis A.
Acta Physica Polonica A
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2002
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vol. 102
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issue 2
329-335
EN
Hot-electron noise is investigated for InGaAs and InAs quantum wells containing a two-dimensional electron gas channel in a pulsed electric field applied parallel to the interfaces. Noise sources resulting from hot-electron "thermal" motion, electron temperature fluctuations, and real-space transfer are observed. The experimental results on hot-electron "thermal" noise are used to estimate energy relaxation time in the field range where other sources do not play any important role. Measurements of noise anisotropy in the plane of electron confinement are used to discuss real-space-transfer noise. High-frequency noise technique is used to study hot-electron trapping, and trap location in InAlAs/InGaAs/InAlAs heterostructure channels is determined.
11
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Tuning of Spectral Sensitivity of AlGaN/GaN UV Detector

80%
Korona K., Drabińska A., Trajnerowicz A., Bożek R., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2003
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vol. 103
|
issue 6
675-681
EN
GaN/AlGaN photodetector that exhibits new interesting property is presented. Its spectral sensitivity depends upon bias voltage. Under positive or low negative bias the detector is sensitive mainly to the ultrafiolet radiation absorbed by AlGaN layer 3.7-3.8 eV. Under negative bias U_B below -4 V, the detector is sensitive mainly to the radiation absorbed by GaN (3.4-3.6 eV). The effect can be explained based on numerical calculations of the electric field and potential profiles of this structure. The damping of GaN signal is attributed to activity of 2D electron gas formed on the GaN/AlGaN interface by spontaneous polarization. The reappearing of the signal is attributed to tunneling of holes through AlGaN, stimulated by a high electric field.
12
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Mesoscopic Structures for Microwave-THz Detection

80%
Sužied.elis A., Ašmontas S., Požela J., Kundrotas J., Širmulis E., Gradauskas J., Kozič A., Kazlauskaité V., Anbinderis T.
Acta Physica Polonica A
|
2008
|
vol. 113
|
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.
13
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Thin Film ZnO as Sublayer for Electric Contact for Bulk GaN with Low Electron Concentration

80%
Grzanka S., Łuka G., Krajewski T., Guziewicz E., Jachymek R., Purgal W., Wiśniewska R., Sarzyńska A., Bering-Staniszewska A., Godlewski M., Perlin P.
Acta Physica Polonica A
|
2011
|
vol. 119
|
issue 5
672-674
EN
Fabrication of low resistivity ohmic contacts to N polarity gallium nitride crystal is an important issue for the construction of the vertical current flow devices like laser diodes and high brightness light emitting diodes. Gallium nitride is a challenging material because of the high metal work function required to form a barrier-free metal-semiconductor interface. In practice, all useful ohmic contacts to GaN are based on the tunneling effect. Efficient tunneling requires high doping of the material. The most challenging task is to fabricate high quality metal ohmic contacts on the substrate because the doping control is here much more difficult that in the case of epitaxial layers. In the present work we propose a method for fabricating low resistivity ohmic contacts on N-side of GaN wafers grown by hydride vapor phase epitaxy. These crystals were characterized by a n-type conductivity and the electron concentration of the order of 10^{17} cm^{-3}. The standard Ti/Au contact turned out to be unsatisfactory with respect to its linearity and resistance. Instead we decided to deposit high-n type ZnO layers (thickness 50 nm and 100 nm) prepared by atomic layer deposition at temperature of 200°C. The layers were highly n-type conductive with the electron concentration in the order of 10^{20} cm^{-3}. Afterwards, the metal contact to ZnO was formed by depositing Ti and Au. The electrical characterization of such a contact showed very good linearity and as low resistance as 1.6 × 10^{-3} Ω cm^2. The results indicate advantageous properties of contacts formed by the combination of the atomic layer deposition and hydride vapor phase epitaxy technology.
14
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Deep Levels in GaN p-n Junctions Studied by Deep Level Transient Spectroscopy and Laplace Transform Deep-Level Spectroscopy

80%
Dyba P., Placzek-Popko E., Zielony E., Gumienny Z., Grzanka S., Czernecki R., Suski T.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
669-671
EN
p^+-n GaN diodes were studied by means of conventional deep level transient spectroscopy and Laplace transform deep-level spectroscopy methods within the temperature range of 77-350 K. Deep level transient signal spectra revealed the presence of a majority and minority trap of indistinguishable signatures. The Laplace transform deep-level spectroscopy technique due to its superior resolution allows us to unambiguously identify and characterize the traps. The apparent activation energy and capture cross-section for the majority trap were found to be equal to 0.63 eV and 2 × 10^{-16} cm^2 and for the minority trap 0.66 eV and 1.6 × 10^{-15} cm^2. It has been confirmed that the Laplace transform deep-level spectroscopy technique is a powerful tool in characterization of the traps of close signatures.
15
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Content available

Multiband GaN/AlGaN UV Photodetector

80%
Korona K., Drabińska A., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2006
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vol. 110
|
issue 2
211-217
EN
We present optical and electrical measurements made on GaN/AlGaN photodetector structure capable to detect three UV ranges, tuned by external voltage. The highest band at energy of about 3.85 eV is nearly independent of bias applied to the Schottky contact. Photosensitivity of the second band at about 3.65 eV changes strongly with the bias. Signal in this range increases about 20 times when the bias changes from 0 V to -4 V. Photosensitivity of the third band (3.4 eV) appears for strong reverse bias (-3 V). Characteristics of the detector are in qualitative agreement with numerical model, however deep centers present in the AlGaN layers cause quantitative discrepancies. The concentration of defects of the order of 10^{16} cm^{-3} was estimated from current transients.
16
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The Role of Hydrostatic Pressure in Electrical Properties of Au/n-GaAs Schottky diodes with Substituted Polyaniline Interfacial Layer

80%
Özdemir A., Abdolahpour Salari M., Kökce A., Uçar N.
Acta Physica Polonica A
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2017
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vol. 132
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issue 3
1118-1121
EN
Au/polymer P2ClAn(H₃BO₃)/n-GaAs Schottky barrier diodes, where P2ClAn stands for poly(2-chloroaniline), have been fabricated. To fabricate Schottky diodes with polymer interface, n-type GaAs wafer was used. The P2ClAn polymer solution was applied on the front face of the n-GaAs wafer by a pipette. The P2ClAn emeraldine salt was chemically synthesized by using boric acid (H₃BO₃). Schottky diode parameters, such as ideality factor, barrier height and series resistance have been measured, as functions of hydrostatic pressure, using the current-voltage technique. The ideality factor values of Au/P2ClAn/n-GaAs Schottky barrier diodes have decreased from 3.38 to 3.01, the barrier height has increased from 0.653 to 0.731 eV at 0.36 kbar and series resistances were ranging from 14.95 to 14.69. The results obtained from I-V characteristics of Au/P2ClAn/n-GaAs Schottky barrier diodes show that pressure treatment improves the rectifying properties of the diodes. These diodes can be used as pressure-sensitive capacitors, due to pressure-dependence of diode parameters.
17
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Pressure Dependence of the Schottky Barrier Heights in Al/AlGaAs Junctions

80%
Dobaczewski L., Langer J., Missous M.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
741-744
EN
The influence of hydrostatic pressure up to 8 kbar on the barrier height of epitaxially MBE-grown Al on AlGaAs metal-semiconductor junctions is reported. The pressure change of the Schottky barrier on n-type AlGaAs is the same as that of the energy gap (for both direct and indirect-gap AlGaAs compositions), while for p-type AlGaAs it is negligible. This result is in direct conflict with a class of models of the Schottky barrier formation based on a concept of a semiconductor neutrality level alignment with the metal Fermi level.
18
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Submillimeter-Wave Oscillations in Recessed InGaAs/InAlAs Heterostructures: Origin and Tunability

80%
Pérez S., Mateos J., González T.
Acta Physica Polonica A
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2011
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vol. 119
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issue 2
111-113
EN
By means of an ensemble Monte Carlo simulator, the appeareance of THz oscillations in InAlAs/InGaAs slot diodes is predicted when the applied bias exceeds the threshold for intervalley transfer. Such high frequency is attained by the presence of a Gunn-like effect in the recess-to-drain region of the device channel whose dynamics is controlled by ballistic Γp valley electrons. In this work we explain the mechanism at the origin of this effect and also the influence of the bias conditions, δ-doping, recess-to-drain distance and recess length on the frequency of the ultrafast Gunn-like oscillations. The simulations show that a minimum value for the δ-doping is necessary to have enough carrier concentration under the recess and allow the oscillations to emerge. Finally, we show that shortening the devices (small recess and recess-to-drain lengths) increases the oscillation frequency, so provides an interesting frequency tunability of this THz source.
19
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The Electric Field and Temperature Dependence of Conductance of Two-Dimensional Electron Gas in AlGaN/AlN/GaN

80%
Ardaravičius L., Kiprijanovič O., Liberis J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
1001-1004
EN
The two-dimensional gas in AlGaN/AlN/GaN heterostucture with a very thin (0.6 nm) AlN spacer was investigated by conductivity relaxation measurements in 86-300 K temperature range. The results show the presence of two exponential relaxation processes characterized by different characteristic time constants. Parameters of the fast and slow components of the processes differently depend on the electric field and temperature. The fast process is attributed to influence of the electric field on the barrier formed by the spacer, while the slow process is attributed to the hot-electron capture out of the channel followed by electron thermal release.
20
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Enhanced Electron Saturated Drift Velocity in AlGaAs/GaAs/AlGaAs Heterostructures

80%
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
|
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.
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