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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 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 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 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 Shallow donors in a quantum well wire: Electric field and geometrical effects(Wiley-V C H Verlag Gmbh, 1997) Ulas, M; Akbas, H; Tomak, MSubband and shallow donor binding energies are calculated. The emphasis is given on the electric field effects for wires of different shapes. It is shown that the donor binding energy is sensitive to the interplay of the electric field and geometrical effects.
