Yazar "Cicek, E." seçeneğine göre listele
Listeleniyor 1 - 11 / 11
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Combined effects of the hydrostatic pressure and temperature on the self-polarization in a finite quantum well under laser field(Academic Press Ltd- Elsevier Science Ltd, 2021) Cicek, E.; Mese, A., I; Ozkapi, B.; Erdogan, IIn this study, the self-polarization and binding energy of the donor impurity atom in the laser field applied Ga1_xAlxAs/GaAs quantum well are investigated under the combined influence of hydrostatic pressure and temperature. Variation of self-polarization and binding energy depending on temperature, hydrostatic pressure, impurity position, well width and laser field parameters are shown. Using the effective mass approximation, subband energy has been found by finite difference method and impurity energy has been found by variation method. Our results showed that hydrostatic pressure and temperature have a noticeable effect on the calculated selfpolarization and binding energy in a quantum well under the effect of the laser field. We think that the results obtained will be useful in determining the physical properties of the quantum well under the influence of laser field, hydrostatic pressure and temperature.Öğe The effect of dielectric constant on binding energy and impurity self-polarization in a GaAs-Ga1-xAlxAs spherical quantum dot(Indian Assoc Cultivation Science, 2017) Mese, A. I.; Cicek, E.; Erdogan, I.; Akankan, O.; Akbas, H.The ground state, 1s, and the excited state, 2p, energies of a hydrogenic impurity in a GaAs-Ga1-xAlxAs spherical quantum dot, are computed as a function of the donor positions. We study how the impurity self-polarization depends on the location of the impurity and the dielectric constant. The excited state anomalous impurity self-polarization in the quantum dot is found to be present in the absence of any external influence and strongly depends on the impurity position and the radius of the dot. Therefore, the excited state anomalous impurity self-polarization can give information about the impurity position in the system. Also, the variation of E-b1s and E-b2p with the dielectric constant can be utilized as a tool for finding out the correct dielectric constant of the dot material by measuring the 1s or 2p state binding energy for a fixed dot radius and a fixed impurity position.Öğe The effects of geometrical shape and impurity position on the self-polarization of a donor impurity in an infinite GaAs/AlAs tetragonal quantum dot(Indian Assoc Cultivation Science, 2021) Akankan, O.; Erdogan, I.; Mese, A. I.; Cicek, E.; Akbas, H.Using the variational method within the effective-mass approximation, the effects of geometrical shape and impurity position on the ground-state self-polarization and binding energy of a donor impurity are theoretically studied for the infinite GaAs/AlAs tetragonal quantum dot. We have found that the ground-state self-polarization and binding energy depend on geometrical shape and impurity-AlAs layer distance.Öğe Laser field effect on the normalized self-polarization, self-polarization and binding energy in square quantum wells made of different materials(Elsevier, 2023) Mese, A. I.; Cicek, E.; Ozkapi, S. G.; Ozkapi, B.; Erdogan, I.In this study, we examine the effect of the laser field on normalized self-polarization, self-polarization, and binding energy in square quantum wells made of four different materials under effective mass approximation. The effects of well width, laser field, and impurity position on normalized self-polarization, self-polarization, and binding energies are shown in detail. The subband energies are obtained by the finite difference method, and the impurity energies are calculated by the variational method. The laser field significantly affects binding energy, self-polarization, and normalized self-polarization. The term normalized self-polarization is defined for the first time in this study. This allows a more detailed examination of the self-polarization change depending on the impurity position. Examining the laser field effect, especially in square quantum wells made of different materials, will provide researchers with helpful information about the importance of material selection in calculating binding energy, self-polarization, and normalized self-polarization.Öğe Modeling of quantum point contacts in high magnetic fields and with current bias outside the linear response regime(Amer Physical Soc, 2008) Arslan, S.; Cicek, E.; Eksi, D.; Aktas, S.; Weichselbaum, A.; Siddiki, A.The electron and current-density distributions in the close proximity of quantum point contacts (QPCs) are investigated. A three-dimensional Poisson equation is solved self-consistently to obtain the electron density and potential profile in the absence of an external magnetic field for gate and etching defined devices. We observe the surface charges and their apparent effect on the confinement potential, when considering the (deeply) etched QPCs. In the presence of an external magnetic field, we investigate the formation of the incompressible strips and their influence on the current distribution both in the linear response and out of linear response regime. A spatial asymmetry of the current carrying incompressible strips, induced by the large source drain voltages, is reported for such devices in the nonlinear regime.Öğe The size effect of the tetragonal quantum dot on the self-polarization under the spatial electric field(Indian Assoc Cultivation Science, 2024) Cicek, E.; Mese, A. I.; Akankan, O.; Akbas, H.In this paper, the effect of the spatial electric field on the hydrogenic impurity self-polarization and binding energy in a GaAs/AlAs tetragonal quantum dot are calculated by the variational method based on the effective mass approximation. We have shown that the self-polarization and binding energy of a hydrogenic impurity in a tetragonal quantum dot depends strongly on the theta angle of the spatial electric field, the size effect (L-z/L ratio (M)), the volume of the dot, and impurity position. Furthermore, we define the angle theta(max), which aligns the spatial electric field vector with the position vector of the hydrogenic impurity on the diagonal axis. It has been noted that self-polarization reaches its peak at this particular angle.Öğe Spatial distribution of the incompressible strips at AB interferometer(Elsevier Science Bv, 2010) Cicek, E.; Mese, A. I.; Ulas, M.; Siddiki, A.In this work, the edge physics of an Aharonov-Bohm interferometer (ABI) defined on a two dimensional electron gas, subject to strong perpendicular magnetic field B, is investigated. We solve the three dimensional Poisson equation using numerical techniques starting from the crystal growth parameters and surface image of the sample. The potential profiles of etched and gate defined geometries are compared and it is found that the etching yields a steeper landscape. The spatial distribution of the incompressible strips is investigated as a function of the gate voltage and applied magnetic field, where the imposed current is confined to. AB interference is investigated due to scattering processes between two incompressible edge-states. (C) 2009 Elsevier B.V. All rights reserved.Öğe Theoretical investigation of the effect of sample properties on the electron velocity in quantum Hall bars(Amer Physical Soc, 2007) Eksi, D.; Cicek, E.; Mese, A. I.; Aktas, S.; Siddiki, A.; Hakioglu, T.We report on our theoretical investigation of the effects of the confining potential profile and sample size on the electron velocity distribution in (narrow) quantum Hall systems. The electrostatic properties of the electron system are obtained by the Thomas-Fermi-Poisson nonlinear screening theory. The electron velocity distribution as a function of the lateral coordinate is obtained from the slope of the screened potential at the Fermi level and within the incompressible strips. We compare our findings with the recent experiments.Öğe Theoretical investigation of the electron velocity in quantum Hall bars, in the out of linear response regime(Elsevier, 2008) Siddiki, A.; Eksi, D.; Cicek, E.; Mese, A. I.; Aktas, S.; Hakioglu, T.We report on our theoretical investigation of the electron velocity in (narrow) quantum Hall systems, considering the out-of-linear-response regime. The electrostatic properties of the electron system are obtained by the Thomas-Fermi-Poisson nonlinear screening theory. The electron velocity distribution as a function of the lateral coordinate is obtained from the slope of the screened potential within the incompressible strips (ISs). The asymmetry induced by the imposed current on the ISs is investigated, as a function of the current intensity and impurity concentration. We find that the width of the IS on one side of the sample increases linearly with the intensity of the applied current and decreases with the impurity concentration. (C) 2007 Elsevier B.V. All rights reserved.Öğe Time-dependent transport in Aharonov-Bohm interferometers(Iop Publishing Ltd, 2012) Kotimaki, V.; Cicek, E.; Siddiki, A.; Rasanen, E.A numerical approach is employed to explain transport characteristics in realistic, quantum Hall-based Aharonov-Bohm (AB) interferometers. Firstly, the spatial distribution of incompressible strips, and thus the current channels, are obtained by applying a self-consistent Thomas-Fermi method to a realistic heterostructure under quantized Hall conditions. Secondly, the time-dependent Schrodinger equation is solved for electrons injected in the current channels. Distinctive AB oscillations are found as a function of the magnetic flux. The oscillation amplitude strongly depends on the mutual distance between the transport channels and on their width. At an optimal distance the amplitude and thus the interchannel transport is maximized, which determines the maximum visibility condition. On the other hand, the transport is fully suppressed at magnetic fields corresponding to half-integer flux quanta. The results confirm the applicability of realistic AB interferometers as controllable current switches.Öğe Where are the edge-states near the quantum point contacts? A self-consistent approach(Elsevier, 2008) Siddiki, A.; Cicek, E.; Eksi, D.; Mese, A. I.; Aktas, S.; Hakioglu, T.In this work, we calculate the current distribution, in the close vicinity of the quantum point contacts (QPCs), taking into account the Coulomb interaction. In the first step, we calculate the bare confinement potential of a generic QPC and, in the presence of a perpendicular magnetic field, obtain the positions of the incompressible edge states (IES) taking into account electron-electron interaction within the Thomas-Fermi theory of screening. Using a local version of Ohm's law, together with a relevant conductivity model, we also calculate the current distribution. We observe that, the imposed external current is confined locally into the incompressible strips. Our calculations demonstrate that, the inclusion of the electron-electron interaction, strongly changes the general picture of the transport through the QPCs. (C) 2007 Elsevier B.V. All rights reserved.
