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1
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Electron and Hole States in Closed Spherical Quantum Dot with Linearly Graded Composition

100%
Kostić R., Stojanović D.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
768-770
EN
The theoretical investigation of the electron and hole spectra in a quantum dot with a linearly graded composition within the effective mass approximation is presented. The particular example is β-HgS surrounded by CdS. β-HgS core of radius r_C is surrounded by concentric spherical layers each of Hg_{1-x}Cd_{x}S composition (x is function of r) and finally, form radius r_S by CdS. The existence of these intermediate layers, as model of graded composition, influences rapidly electron and hole spectra.
2
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Study of Spin-Orbit Coupling Effect on Bismuth (111) Bilayer

100%
Bieniek M., Woźniak T., Potasz P.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
609-612
EN
Band inversion process in Bi(111) bilayer is studied using many-orbital tight-binding model, supported by the density-functional theory calculations, with a controllable spin-orbit coupling constant in tight-binding model. This effect is important in order to verify a topological nature of this material. We show that after closing of the energy gap leading to crossing of the valence and conduction bands, the second band inversion occurs within a valence band. We analyze orbital composition and spin textures of bands within different regimes. Around a Γ point, all spins align in one direction before the first band inversion. Moreover, a change of signs for some spin components after a band inversion is noticed. After the second band inversion, a significant change of orbital contribution of the top of the valence band is observed.
3
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Polarization-Induced Band Inversion in In-Rich InGaN/GaN Quantum Wells

100%
Łepkowski S., Bardyszewski W., Rodak D.
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vol. 126
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issue 5
1154-1155
EN
We theoretically study the polarization-induced band inversion phenomenon in c-plane In-rich InGaN/GaN quantum wells. Our calculations performed using the k·p method with the 8×8 Rashba-Sheka-Pikus Hamiltonian for the structures with the indium content between 90% and 100% show that the reordering of the conduction and valence bands occurs for the quantum well widths below the theoretical values of critical thickness for InGaN layers pseudomorphically grown on GaN substrates.
4
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Multiple Exciton Generation in InAs Nanocrystals

100%
Kowalski P., Machnikowski P.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1187-1192
EN
We study a simple theoretical model of multiple exciton generation by a single high-energy photon absorbed in an InAs nanocrystal. We calculate the Coulomb matrix element for the electron-trion coupling in an InAs nanocrystal and show that due to the resulting coupling between single-pair and two-pair states the latter becomes weakly optically active.
5
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Influence of Geometric-Confinement Parameters on the Electronic Properties of Quantum Ring

80%
Moskal S., Spisak B.
Acta Physica Polonica A
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2007
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vol. 112
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issue 1
101-112
EN
We investigate the electronic properties of the quantum rings modelled by a two-dimensional non-singular potential with the cylindrical symmetry as well as the influence of the potential's parameters on energy spectra. In the presence of the external magnetic field we also calculated the persistent currents in such structures in the ballistic regime.
6
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Excitonic Magnetoabsorption of Cylindrical Quantum Disks

80%
Schillak P., Czajkowski G.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
888-890
EN
We show how to compute the optical functions (the complex magnetosusceptibility, dielectric function, magnetoreflection) for semiconductor quantum disks exposed to a uniform magnetic field in the growth direction, including the excitonic effects. The method uses the microscopic calculation of nanostructure excitonic wave functions and energy levels, and the macroscopic real density matrix approach to compute the electromagnetic fields and susceptibilities. The electron-hole screened Coulomb potential is adapted and the valence band structure is taken into account in the cylindrical approximation, thus separating light- and heavy-hole motions. The confinement potentials are taken as step-like both in the z and in-plane directions. Numerical calculations have been performed for In_{0.55}Al_{0.45}As (disk)/Al_{0.35}Ga_{0.65}As (barrier) and InP/GaP disks and the results are in a good agreement with the available experimental data.
7
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Electron and Exciton Quasi-Stationary s-States in Open Spherical Quantum Dots

80%
Tkach M., Seti J., Voitsekhivska O.
Acta Physica Polonica A
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2012
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vol. 122
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issue 1
207-211
EN
The theoretical calculation of spectral parameters of electron and exciton quasi-stationary s-states in open spherical quantum dot is performed within the effective mass approximation and rectangular potentials model. The conceptions of probability distribution functions (over quasi-momentum or energy) of electron location inside of quantum dot and their spectral characteristics: generalized resonance energies and widths are introduced. It is shown that the generalized resonance energies and widths, obtained within the distribution functions, satisfy the Heisenberg uncertainty principle for the barrier widths varying from zero to infinity. At the same time, the ordinary resonance energies and widths defined as complex poles of scattering S-matrix, do not satisfy it for the small barrier widths and, therefore, are correct only for the open quantum dots with rather wide potential barriers.
8
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Oblique Reflection of Electrons from a Potential Barrier in Heterostructures

80%
Pfeffer P., Zawadzki W.
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vol. 126
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issue 3
820-827
EN
Reflection of electrons from a potential barrier in heterostructures is described. An electric field of the barrier causes spin splitting of electron energies via the spin-orbit interaction and its form is calculated in the three-level k·p model for a nontrivial case of unbound electrons. It is shown that if the potential barrier is the only source of the spin-orbit interaction, the spin-flip electron reflections are not possible. However, there appear two unexpected possibilities related to the spin-orbit interaction: (a) non-attenuated electron propagation in the barrier whose height exceeds the energies of incoming electrons, (b) total reflection of electrons whose energies exceed barrier's height. It is indicated that the system can serve as a source of spin-polarized electron beams.
9
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Novel Approach for Energy Spectrum Probing in Semiconducting Quantum Dots

80%
Zdrojek M., Wąsik M., Esplandiu M., Bachtold A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
321-323
EN
A new technique has been used to probe the electronic properties of quantum dots. Here we discuss the case of semiconducting CdSe dots. This technique allows us to fill (or empty) semiconducting quantum dot with many electrons. The detection scheme is based on an original approach where the investigated particle is attached to only one electrode, a carbon nanotube. The conductance of the nanotube is measured as a function of a gate voltage (V_{g}), which allows the detection of individual electrons transferred onto the quantum dot. For certain range of V_{g} we noticed no electron transfer which is attributed to the energy gap of the CdSe quantum dot. Our study shows that single-electron detection with carbon nanotube transistor represents a new strategy to study the separation between the electronic discrete energy levels of the semiconducting quantum dot.
10
Content available remote

Electronic Structure Calculations of InP-Based Coupled Quantum Dot-Quantum Well Structures

80%
Andrzejewski J.
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EN
In this work we investigate the electronic structure of coupled 0D-2D nanostructures. The respective confined state energy levels in a quantum dot-quantum well system are calculated for various conduction band offsets - between the quantum dot and surrounding material. The calculated electron and hole energy levels with their wave functions allow determining if the wave functions are within the injector quantum well or within the quantum dot and if the carrier positions on the energy scale are appropriate from the point of view of a possible laser structure utilizing the so-called tunnel injection scheme. It is shown that for an adequate width of an injector quantum well and the conduction band offsets designing an optimal tunnel injection structure is possible.
11
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Surface Electronic Properties of Fe Nanoparticles on c(2×2)-N/Cu(001)

70%
Getzlaff M., Bode M., Wiesendanger R.
Acta Physica Polonica A
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2003
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vol. 104
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issue 3-4
327-335
EN
We prepared nanoscaled particles consisting of ferromagnetic material on a nanostructured template. This nanolithographic procedure allows to fabricate high-density magnetic nanodots in a highly ordered way. For this purpose, Fe particles were grown on the c(2×2)-N/Cu(001) surface which exhibits a checkerboard-like structure. Scanning tunneling spectroscopic measurements demonstrate that the electronic properties of the areas with deposited material are identical to clean copper. Fe nanoparticles on the reconstructed patches show a significantly different electronic behavior. These observations directly hint to a covering of iron with copper on the clean surface.
12
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Determination of Quantum Dot Morphology from Magnetooptical Properties

61%
Křápek V., Schliwa A., Bimberg D.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
339-343
EN
We present here the calculations of magnetooptical properties in InAs/GaAs quantum dots with different shapes, including excitonic effects. The influence of several structural parameters, such as vertical profile, aspect ratio, and basis squareness is discussed, as well as the possibility to retrieve the structural parameters from magnetooptical measurements.
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