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1
Content available remote

Stark Effect for Donors in Double Quantum Wells

100%
Rolnik S., Adamowski J.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
893-896
EN
The problem of a hydrogenic donor in a semiconductor double quantum well under a homogeneous electric field is studied by variational means. The energy levels corresponding to the quantum states 1s, 2s, 2p have been calculated with the help of the many-element variational basis consisting of the exponential functions. The influence of the electric field on the donor binding energy is determined for different impurity positions. The 1s-2p transition energies have been calculated for a possible comparison with experiment.
2
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Infrared Absorption on Shallow Donors in CdF_{2}

100%
Bednarek S., Adamowski J.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 2-3
393-396
EN
A theoretical description of shallow donor absorption spectra in CdF_{2} in the infrared region is given. The properties of the stable (Y) and bistable (In) donors are analyzed and quantatively described. It is shown that the bistability of donors and the shape of the infrared absorption band have the same origin, which is the combined effect of electron-LO-phonon coupling, conduction band non-parabolicity and short-range central-cell potential.
3
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New Donor State of S Symmetry

100%
Bednarek S., Adamowski J.
Acta Physica Polonica A
|
1993
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vol. 84
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issue 4
820-822
EN
The influence of the short-range potential and the electron-phonon coupling on the donor spectrum is discussed. It is shown that the attractive short-range potential leads to a formation of a single additional state of s symmetry and with energy lying below a weakly perturbed hydrogen-like spectrum, which includes the 1s level. The new state can be called the 0s state. With decreasing short-range attraction, the energy of this state increases crossing over the hydrogen-like levels and, for weak short-range potential, the 0s state disappears. If the electron-phonon coupling is sufficiently strong, the donor hydrogen-like spectrum is perturbed only in a very narrow region of the leve1 crossing.
4
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Anion-Cation Site Dependence of Pressure Coefficients for Donors in GaAs

100%
Bednarek S., Adamowski J.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
671-674
EN
The theoretical model, based on the many-band approach, is proposed for the strongly localized donor states in GaAs. The pressure coefficients for the states of A_{1} and Τ-2 symmetry have been calculated for the donors at the anion and cation sites. The obtained results show that these pressure coefficients are different from the conduction-band pressure coefficients and are dependent on the lattice site occupied by the impurity as well as on the symmetry of the donor states.
5
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Effect of Electric and Magnetic Fields on Donor States in Semiconductor Quantum Wells

100%
Rolnik S., Adamowski J.
Acta Physica Polonica A
|
1996
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vol. 90
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issue 5
915-918
EN
An influence of static external electric and magnetic fields on donor states in a quantum well is studied by variational means. The energies of the 1s and 2p_{±} hydrogenic states were calculated for different structure parameters (well depth and width) and different fields applied. The calculated 1s-2p_{±} transition energies agree well with experimental data.
6
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Conduction Band Influence on the Properties of Bistable Donors

100%
Bednarek S., Adamowski J.
Acta Physica Polonica A
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1991
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vol. 80
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issue 3
357-360
EN
A theoretical description of bistable donors in polar semiconductors is proposed. The donor states are described within the one-band approximation, which takes into account a finite width and nonparabolicity of the conduction band. The interaction between the defect and the crystal lattice is assumed in the Fröhlich form. For the bistable indium impurity in cadmium fluoride, a coexistence of strongly and weakly localized donor states has been obtained. The calculated energies for both the states and absorption band shape in the 3-eV range are in agreement with experiment.
7
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Metastable One- and Two-Electron donor States in GaAs and CdF_{2}

100%
Bednarek S., Adamowski J.
Acta Physica Polonica A
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1996
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vol. 90
|
issue 4
719-722
EN
The strongly localized one-electron (D^{0}) and two-electron (D¯) donor states are considered with the lattice deformation around the donor center taken into account. For GaAs, the donor energy levels have been calculated as functions of the hydrostatic pressure. The calculated energy positions and pressure coefficients agree with the experimental data. It is shown that the interaction with phonons reduces the probability of radiative transitions between the states of different localization and leads to the metastability of shallow-level donor states with respect to the D¯ state in GaAs and both the states (D^{0} and D¯) in CdF_{2}.
8
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Two-Electron Quantum Dots in Magnetic Field

100%
Adamowski J., Spisak B.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 4
695-698
EN
A theoretical description is given for electronic properties of semiconductor quantum dots in a magnetic field. A two-electron model is applied for electrons in a cylindrical quantum dot with a parabolic confinement potential. The eigenvalue problem is solved by the variational method with the trial wave function proposed in the form of linear combination of S-type and P-type Gaussians. The energy levels of singlet and triplet states with arbitrary radial and magnetic quantum numbers have been calculated as a function of the applied magnetic field. The calculated cyclotron transition energies agree well with those measured for InGaAs/GaAs quantum dots. It is shown that the electron-electron interaction has a small influence on the transition energy.
9
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Computer Simulations of Electron Transport through a Nanowire Quantum Dot

81%
Łapa D., Sowa A., Adamowski J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1213-1218
EN
Electron tunneling through a quantum dot embedded in a nanowire was studied by the transfer matrix method. A smoothness of the interfaces was taken into account using the analytical parametrization of the potential profile. We calculated the current-voltage characteristics and discussed the effect of the spacer, which separates the quantum dot from the contacts. We found that the tunneling current peak possesses the asymmetric Fano resonance shape in the absence of spacer. The results of calculations agree with the experimental data.
10
Content available remote

Theoretical Description of Shell Filling in Cylindrical Quantum Dots

81%
Szafran B., Bednarek S., Adamowski J.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
555-559
EN
A theoretical quantitative description is given for non-periodic oscillations observed in a current vs. gate voltage characteristics of cylindrical quantum dots. Energy eigenvalues and chemical potentials for a system of N confined electrons (N=1,...,13) are calculated by the unrestricted Hartree-Fock method with a confinement potential proportional to the gate voltage. The positions of the observed peaks of the current are reproduced with a very good accuracy. The non-periodicity of the characteristic is explained as a result of the shell filling, which is a signature of the quantum Coulomb blockade.
11
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Simulation of Spin-Dependent Electronic Transport through Resonant Tunnelling Diode with Paramagnetic Quantum Well

81%
Wójcik P., Spisak B., Wołoszyn M., Adamowski J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
648-650
EN
The spin-dependent electronic transport is investigated in a paramagnetic resonant tunnelling diode formed from Zn_{1 - x}Mn_{x}Se quantum well between two ZnBeSe barrier layers. The spin-dependent current-voltage characteristics have been obtained in the presence of magnetic fields by solving the quantum kinetic equation for the Wigner distribution function and the Poisson equation in the self-consistent procedure. We have obtained two distinct current peaks due to the giant Zeeman splitting of electronic levels in a qualitative agreement with experiment. We have shown that the sign of spin current polarization can be reversed by tuning the bias voltage. Moreover, we have found the bias voltage windows with a nearly constant polarization.
12
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Application of Non-Classical Distribution Function to Transport Properties of Semiconductor Nanodevices

81%
Wójcik P., Spisak B., Wołoszyn M., Adamowski J.
Acta Physica Polonica A
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2008
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vol. 114
|
issue 5
1431-1436
EN
The non-classical distribution function formalism is used for studying the electron transport in a nanosystem. We calculated the current-voltage characteristics of a triple barrier one-dimensional nanostructure which is connected to three-dimensional (highly doped semiconductor) reservoirs by the ohmic contacts. We also estimated the peak-to-valley ratio for the considered nanostructure and discussed the effect of switching the bias from peak-to-valley and from valley-to-peak voltages.
13
Publication available in full text mode
Content available

Transport and Capacitance Spectroscopy of Quantum Dots

81%
Adamowski J., Bednarek S., Szafran B.
Acta Physica Polonica A
|
2001
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vol. 100
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issue 2
145-163
EN
A review of recent theoretical studies on a single-electron tunneling in quantum dots is presented. This effect underlies the transport spectroscopy performed on the vertical gated quantum dots and the capacitance spectroscopy on the self-assembled quantum dots. The conditions of the single-electron tunneling are formulated in terms of electrochemical potentials of the electrons in the leads and in the quantum dot. The electrochemical potentials for the electrons confined in the quantum dots can be calculated by solving the many-electron Schrödinger equation. The results obtained by the Hartree-Fock method are presented. For the vertical gated quantum dot, the realistic confinement potential is obtained from the Poisson equation. The application of the self-consistent procedure to the solution of the Poisson-Schrödinger problem is discussed. The calculated positions of the current peaks at zero bias and boundaries of the Coulomb diamonds for non-zero bias are in good agreement with experiment. The influence of an external magnetic field on the single-electron tunneling is also discussed. The spin-orbital configurations of the electrons confined in the quantum dots change with the magnetic field, which leads to features observed in the current-voltage and capacitance-voltage characteristics.
14
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Spin Conductance of Nanowires with Double Coupled Quantum Dots

81%
Wołoszyn M., Spisak B., Wójcik P., Adamowski J.
|
EN
Using the computer simulations we have studied the spin conductance of the InAs nanowire with three all-around gates that generate two coupled quantum dots in the nanowire. We have assumed that the same constant voltage is applied to the outermost (left and right) gates and investigated the effect of the varying central-gate voltage (V_{G}) and axially directed magnetic field B on the spin currents. The calculated spin-up and spin-down conductances exhibit pronounced oscillations as functions of V_{G}. In certain intervals of V_{G}, both the spin conductances oscillate in antiphase, which can be applied to the spin-filter operation.
15
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Electron Pairs and Excitons in Quasi-One-Dimensional Nanostructures

81%
Bednarek S., Szafran B., Chwiej T., Adamowski J.
Acta Physica Polonica A
|
2003
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vol. 103
|
issue 6
567-572
EN
A theoretical study of two-particle systems in quasi-one-dimensional quantum wires and quantum dots is presented. We have derived the analytical formula for the effective interaction potential between the charge carriers confined laterally by a strong parabolic potential and applied this formula to electron pairs in single and double quantum dots and to excitons in quantum wires. In the single quantum dot of the sufficiently large size, we have found the Wigner-type localization.
16
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Influence of Geometrical Parameters on the Transport Characteristics of Gated Core-Multishell Nanowires

71%
Palutkiewicz T., Wołoszyn M., Wójcik P., Adamowski J., Spisak B.
|
EN
Calculations of the current-voltage characteristics of the core-multishell nanowires for different radii of the core and various thicknesses of the shells are presented. A role of the conducting core and shells in the coherent transport under the influence of the gate voltage is discussed.
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