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Öğe Acceptor 1s-2p± transitions in GaAs/Ga0.7Al0.3As quantum wells(Wiley-V C H Verlag Gmbh, 1998) Akbas, H; Aktas, S; Okan, SE; Ulas, M; Tomak, MThe valence subband energies in the presence of an electric-field are calculated using the fourth-order Runge-Kutta method. The 1s- and 2p(+/-)-like acceptor states in the presence of a magnetic field are then calculated variationally. The effects of the spatially dependent screening function epsilon(r) on the calculation of the transition energies are specifically investigated. The use of a constant epsilon(o) is shown to yield better agreement with experimental results.Öğe Anomalous polarization in an electric field and self-polarization in GaAs/AlAs quantum wells and quantum well wires(Elsevier Science Bv, 2004) Okan, SE; Erdogan, I; Akbas, HThe response of an electron to an electric field in the infinite quantum wells and the infinite quantum well wires is investigated. Also the self-polarization effect, which can be defined as the influence of the well potential on the impurity electron, is studied for the same structures. The anomalous polarization in the excited states is found to be always exist in the presence of an electric field. Also it is shown that the external electric field polarization is intensified or weakened by an impurity ion depending on its position in the structure. (C) 2003 Elsevier B.V. All rights reserved.Öğe Binding energies of helium-like impurities in parabolic quantum wells under an applied electric field(Academic Press Ltd, 2000) Okan, SE; Akbas, H; Aktas, S; Tomak, MWe present a variational method to compute the binding energies of helium-like impurities in finite parabolic GaAs-Ga1-xAlxAs quantum wells. The effects of band nonparabolicity in the conduction band are taken into account within the effective mass approximation. The dependence of the impurity binding energy on the applied electric field and the impurity position is also discussed together with the polarization effect for all cases. (C) 2000 Academic Press.Öğe Binding energy of relativistic hydrogenic impurities in cylindrical quantum well wires under an applied electric field(Wiley-V C H Verlag Gmbh, 2004) Mese, AI; Okan, SEThe ground state binding energy of a hydrogenic impurity in infinite cylindrical GaAs quantum well wires subjected to an external electric field applied perpendicular to the symmetry axis of the wire is studied within the relativistic approach. A rapid decrease of the binding energy for different intensities of the electric field with increasing wire radius is predicted. Furthermore. the relativistic effects are emphasised by comparing them with the non-relativistic results. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Donor binding energies in GaAs quantum wells considering the band nonparabolicity effects and the wavefunction elongation(Academic Press Ltd, 2000) Aktas, S; Okan, SE; Erdogan, I; Akbas, H; Tomak, MThe donor binding energies in finite GaAs/GaxAl1-As-x quantum wells have been calculated by considering the confinement of electrons, which increases as the well width increases. The variational solutions have been improved by using a two-parameter trial wavefunction, and by including the conduction band nonparabolicity. It is shown that the method used gives results in agreement with those obtained in the experiments on the effective mass and the donor binding energy, both of which are strongly dependent on the well width. (C) 2000 Academic Press.Öğe Electric field effect on the binding energy of a hydrogenic impurity in coaxial GaAs/AlxGa1-xAs quantum well-wires(Academic Press Ltd Elsevier Science Ltd, 2001) Aktas, S; Okan, SE; Akbas, HThe ground state binding energy of a hydrogenic impurity in a coaxial cylindirical quantum well wire system subjected to an external electric field applied perpendicular to the symmetry axis of the wire system is studied within a variational scheme. Binding energy calculations were performed as functions of the inner barrier thickness and the electric field for two different impurity positions. The main result is that a sharp decrease in the binding energy, which may be important in device applications, occurs in certain conditions. (C) 2001 Academic Press.Öğe The exciton transition energies in symmetric double GaAs/AlxGa1-xAs quantum wells(Wiley-V C H Verlag Gmbh, 1999) Okan, SE; Aktas, S; Akbas, H; Tomak, MThe exciton transition energies between valence and conduction subbands of symmetric double quantum wells are studied. To study the effect of geometry coupled wells of rectangular, graded and parabolic shapes are considered. A special emphasis is given to the study of crossover between the symmetric light-hole (e1-11) and the antisymmetric heavy-hole (e2-h2) transitions.Öğe Screening effect on the binding energies of shallow donors, acceptors and excitons in finite-barrier quantum wells(Academic Press Ltd, 1998) Akbas, H; Aktas, S; Okan, SE; Ulas, M; Tomak, MThe conduction and valence subband energies in the presence of an electric field are calculated using the fifth-order Runge-Kutta method. The binding energies of shallow donors, accepters and excitons in finite-barrier GaAs/Ga1-xAlx As quantum wells are then obtained variationally in the presence of a magnetic field. The effects of a spatially dependent screening function epsilon(r) On the calculation of binding energies are specifically investigated. The use of epsilon(r) in comparison with the use of a constant epsilon(0) increases the binding energy of accepters as the increase on shallow donors and excitons is quite small. (C) 1998 Academic Press Limited.Öğe Spatial electric field effect in GaAs-AlAs quantum wires(Elsevier Science Bv, 2005) Akankan, O; Okan, SE; Akbas, HThe response of an electron to a three-dimensional electric field in an infinite quantum well wire of square cross-section is investigated within a variational scheme. The ionization energy and the polarization are calculated for different locations of impurity ion. It is found that the results for the spatial electric field differ from the previous results found for the electric field applied in the direction perpendicular to the wire axis. The ionization energy weakens rapidly with the axial component of the field as the polarization of the carrier distribution intensifies. (C) 2004 Elsevier B.V. All rights reserved.
