Yazar "Radu, A." seçeneğine göre listele

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    Effects of Geometry on the Electronic Properties of Semiconductor Elliptical Quantum Rings
    (NATURE PUBLISHING GROUP, 2018) Vinasco, J. A.; Radu, A.; Kasapoglu, E.; Restrepo, R. L.; Morales, A. L.; Feddi, E.; Mora-Ramos, M. E.; Duque, C. A.
    The electronic states in GaAs-AlxGa1-xAs elliptically-shaped quantum rings are theoretically investigated through the numerical solution of the effective mass band equation via the finite element method. The results are obtained for different sizes and geometries, including the possibility of a number of hill-shaped deformations that play the role of either connected or isolated quantum dots (hills), depending on the configuration chosen. The quantum ring transversal section is assumed to exhibit three different geometrical symmetries - squared, triangular and parabolic. The behavior of the allowed confined states as functions of the cross-section shape, the ring dimensions, and the number of hills-like structures are discussed in detail. The effective energy bandgap (photoluminescence peak with electron-hole correlation) is reported as well, as a function of the Al molar fraction.
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    Electronic states in GaAs-(Al, Ga) As eccentric quantum rings under nonresonant intense laser and magnetic fields
    (NATURE PUBLISHING GROUP, 2019) Vinasco, J. A.; Radu, A.; Niculescu, E.; Mora-Ramos, E.; Feddi, E.; Tulupenko, V.; Restrepo, R. L.; Kasapoglu, E.; Morales, A. L.; Duque, C. A.
    The features of the electron energy spectrum in eccentric two-dimensional GaAs-AlGaAs quantum rings of circular shape are theoretically investigated taking into account the effect of externally applied magnetic and intense laser fields. Analytical expressions for the laser-dressed confining potential in this kind of quantum ring geometry are reported for the first time. Finite element method is used to solve the resulting single-particle effective mass two-dimensional partial differential equation. It is shown that the allowed level spectrum is greatly influence by the external probe as well as by the breaking of geometric symmetry related to the changes in eccentricity. In presence of an intense laser field, the conduction band confining profile suffers strong modifications along the structure, with an additional contribution to symmetry breaking. These modifications of electronic quantum states reflect in the intraband optical absorption. Accordingly, the features of the intraband transitions are discussed in detail, revealing the significant influence of the magnetic field strength and laser field intensity and polarization, together with eccentricity, in the allowing of ground-to-excited states transitions and their corresponding intensities.
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    Theoretical study of electronic and optical properties in doped quantum structures with Razavy confining potential: effects of external fields
    (Springer, 2022) Dakhlaoui, Hassen; Gil-Corrales, J. A.; Morales, A. L.; Kasapoglu, E.; Radu, A.; Restrepo, R. L.; Tulupenko, V
    We investigate the energy states of confined electrons in doped quantum structures with Razavy-like confining potentials. The theoretical investigation is performed within the effective mass and parabolic band approximations, including the influence of externally applied electric and magnetic fields. First, we analyze the case of a Razavy quantum well and determine its conduction subband spectrum, focusing on the lowest energy levels and their probability densities. These properties have been numerically determined by self-consistently solving the coupled system of Schrodinger, Poisson, and charge neutrality equations. Doping is introduced via an on-center delta-like layer. In order to evaluate the associated total (linear plus nonlinear) optical absorption coefficient (TOAC), we have calculated the corresponding diagonal and off-diagonal electric dipole matrix elements, the main energy separation, and the occupancy ratio which are the main factors governing the variation in this optical response. A detailed discussion is given about the influence of doping concentration as well as electric and magnetic fields, which can produce shifts in the light absorption signal, toward either lower or higher frequencies. As an extension of the self-consistent method to a two-dimensional problem, the energy states of quantum wire system of circular cross section, with internal doping and Razavy potential, have been calculated. The response of eigenvalues, self-consistent potentials and electron densities is studied with the variation in delta-doping layer width and of the donor density. Finally, the origin of Friedel-like oscillations, that arise in the density profile, generated by the occupation of internal and surface electronic states has been explained.