DSpace Repository :: Browsing by Author "Porras Montenegro, Nelson"

Browsing by Author "Porras Montenegro, Nelson"

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Aluminum concentration and magnetic field effects on the Landé g factor in GaAs–(Ga,Al)As cylindrical quantum well wires
(2010-02) Mejía Salazar, Jorge Ricardo; Mulato Gómez, D. F.; Porras Montenegro, Nelson
We have performed a theoretical study of the Aluminum concentration and axis-parallel applied magnetic-field effects on the conduction-electron Landé g factor in GaAs–(Ga,Al)As cylindrical quantum well wires. Numerical calculations are performed by using the Ogg–McCombe effective Hamiltonian, which includes nonparabolicity and anisotropy effects for the conduction-band electrons. The quantum wire is assumed to consist of an infinite length cylinder of GaAs, surrounded by Ga1−xAlxAs barrier. Theoretical results are given as functions of the Al concentration, radius and applied magnetic fields. We have studied the competition between the quantum-confinement (geometrical and barrier-potential confinements) and the magnetic field, finding that in this type of heterostructure the effects of the applied magnetic field are very small as compared with the Al concentration and geometrical-confinement effects. Present theoretical results are in very good agreement with previous theoretical findings for x=0.35.
Control cuántico de las propiedades electrónicas y de espín en nanoestructuras inorgánicas, orgánicas y biológicas
(2011-06) Calero Quintero, Jesús María; Granada Echeverri, Juan Carlos; Porras Montenegro, Nelson; Reina Estupiñán, John Henry; Arce Clavijo, Julio César; Pasaje Salcedo, Alfredo; Noguera Yañez, Herlis Arturo
Efectos cuánticos de tamaño en las propiedades físicas de heteroestructuras semiconductoras de baja dimensionalidad del tipo II-V y II-VI"
(Universidad del Valle, 1999-05) Porras Montenegro, Nelson; Granada E., Juan Carlos
Se presenta el informe fmal del proyecto EFECTOS CUANTICOS DE TAMAÑO EN LAS PROPIEDADES FÍSICAS DE HETEROESTRUCTURAS SEMICONDUCTORAS DE BAJA v DIMENSIONALIDAD DEL TIPO 11- V Y 11-VI . En la realización de este proyecto participaron dos profesores del departamento de física de la Universidad del Valle, tres asesores internacionales y colaboradores de la Universidad Industrial de Santander. En el desarrollo del plan de trabajo aprobado participaron además tres estudiantes de doctorado, seis de maestría y cuatro de pregrado, los cuales sustentaron exitosamente sus tesis durante el desarrollo de este proyecto. En el informe académico se muestra que los compromisos adquiridos con COLCIENCIAS fueron cumplidos, de lo cual dan fe 20 artículos internacionales y 18 nacionales. También se indican las diversas actividades realizadas por el grupo, tales como seminarios internos, participación en eventos nacionales e internacionales, organización de eventos y visitas de intercambio tanto nacionales como internacionales. La información sobre el desarrollo del proyecto se complementa con tres anexos, en el primero de los cuales se indica el nombre de responsables, títulos y resúmenes de las tesis realizadas en el Grupo de Física Teórica del Estado Sólido durante la ejecución del proyecto. En el segundo anexo se presentan las copias de los artículos publicados en revistas internacionales y nacionales durante la ejecución del proyecto. Finalmente en el anexo 3 se presenta el informe financiero.
Estados excitados de impurezas y propiedades colectivas en heteroestructuras semiconductoras
(Universidad del Valle, 1998-09) Porras Montenegro, Nelson; Granada E., Juan Carlos
Se presenta un informe del proyecto referenciado. En la realización de este proyecto participaron dos profesores del Departamento de Física de la Universidad del Valle y tres asesores internacionales. En el desarrollo del plan de trabajo aprobado participaron además once estudiantes que realizaron sus trabajos de pregrado (7 tesis) y maestría (cuatro tesis). Además en el marco de la presente investigación se iniciaron dos tesis de doctorado. En el informe académico se muestra que los compromisos adquiridos con COLCIENCIAS fueron cumplidos, de lo cual dan fe 18 publicaciones nacionales y 17 publicaciones internacionales. Se indican las diversas actividades realizadas por el Grupo de investigación conformado, tales como seminarios internos, participación y organización de eventos, etc.
Hydrostatic pressure effects on electron states in GaAs–(Ga,Al) As double quantum rings
(2009-05) Culchac, Francisco; Porras Montenegro, Nelson; Latge, Andrea
Here we address a theoretical analysis of the effects of applied hydrostatic pressure on electron states in concentric GaAs–(Ga,Al)As double quantum rings, under axial magnetic fields. Emphasis is put on the dependence of such effects on the system geometry confinement described within a hard potential model and following an effective-mass approximation. The energy of the ground and excited electronic states were found to decrease with the applied hydrostatic pressure, due mainly to an effective reduction in the barrier potential confinement. Also, while the increase in the magnetic field opens the electron states degeneracy with different angular momenta, the increase in the applied hydrostatic pressure does not alter significantly the energy of these states. For both symmetric and asymmetric double quantum rings, one found that the electron-heavy hole transition energies augment with the applied hydrostatic pressure, mainly due to the increase in the GaAs gap.
Hydrostatic pressure effects on the Landé g∥ factor in GaAs–Ga1−xAlxAs quantum heterostructures under applied magnetic fields
(2010-04) Mejía Salazar, Jorge Ricardo; Porras Montenegro, Nelson
We have performed a theoretical study of the hydrostatic pressure effects on the conduction-electron Landé g∥ factor in GaAs–Ga1−xAlxAs quantum heterostructures (QHs) under the influence of applied magnetic fields. Numerical calculations are performed by using the Ogg–McCombe effective Hamiltonian, which include nonparabolicity and anisotropy effects for the conduction-band electrons. The QHs is assumed to consist of a finite-length cylinder of GaAs surrounded by Ga1−xAlxAs barrier. Theoretical results are given as functions of the radii, lengths, hydrostatic pressure, and applied magnetic fields. We have studied the competition between the geometrical and magnetic confinement versus hydrostatic pressure effects, finding that the geometrical confinement commands the behavior of the g∥ factor. Present theoretical results are in very good agreement with previous experimental and theoretical reports in GaAs–Ga1−xAlxAs heterostructures.
Laser-dressing and magnetic-field effects on shallow-donor impurity states in semiconductor GaAs–Ga1−xAlxAs cylindrical quantum-well wires
(2010-01) López, F. E.; Reyes Gómez, E.; Porras Montenegro, Nelson; Brandi, H. S.; Oliveira, L. E.
The influence of an intense laser field on shallow-donor states in cylindrical GaAs–Ga1−xAlxAs quantum-well wires under an external magnetic field applied along the wire axis is theoretically studied. Numerical calculations are performed in the framework of the effective-mass approximation, and the impurity energies corresponding to the ground state and 2p ± excited states are obtained via a variational procedure. The laser-field effects on the shallow-donor states are considered within the extended dressed-atom approach, which allows one to treat the problem 'impurity + heterostructure + laser field + magnetic field' as a renormalized 'impurity + heterostructure + magnetic field' problem, in which the laser effects are taken into account through a renormalization of both the conduction-band effective mass and fundamental semiconductor gap.
Laser-dressing effects on the electron g factor in low-dimensional semiconductor systems under applied magnetic fields
(2009-05) López, F. E.; Reyes Gómez, E.; Brandi, H. S.; Porras Montenegro, Nelson; Oliveira, L. E.
The effects of a laser field on the conduction-electron effective Landé g factor in GaAs–Ga1−xAlxAs quantum wells and quantum-well wires under applied magnetic fields are studied within the effective-mass approximation. The interaction between the laser field and the semiconductor heterostructure is taken into account via a renormalization of the semiconductor energy gap and conduction-electron effective mass. Calculations are performed for the conduction-electron Landé factor and g-factor anisotropy by considering the non-parabolicity and anisotropy of the conduction band. Theoretical results are obtained as functions of the laser intensity, detuning and geometrical parameters of the low-dimensional semiconductor heterostructures, and indicate the possibility of manipulating and tuning the conduction-electron g factor in heterostructures by changing the detuning and laser-field intensity.
Magnetoexcitons bound to ionized-donor impurities in GaAs/AlxGa1−xAs quantum wells
(2010-11) Vivas Moreno, José Joaquin; Porras Montenegro, Nelson
The binding energy of Wannier excitons bound to ionized-donor impurities, D+, in GaAs/AlxGa1−xAs quantum-wells, is studied using the effective-mass approximation within a variational approach, as a function of the well width for different barrier heights and growth-direction applied magnetic fields. Our calculations are devoted to heavy-hole magnetoexcitons. As expected, we found that the binding energy of a heavy-hole exciton bound to a donor-ionized impurity increases with the Al concentration, as well as with the applied magnetic field. Otherwise, we found that it is higher than the corresponding for heavy-hole excitons without impurities reported by other authors. Moreover we found that the binding energy of the heavy-hole exciton bound to a donor-ionized impurity is higher (lower) for larger (smaller) quantum well width. Finally we found that our results are in very good agreement when we compare with experimental and theoretical reports.
Plasmon polaritons in 1D Cantor-like fractal photonic superlattices containing a left-handed material
(2011-06) Mejía Salazar, Jorge Ricardo; Porras Montenegro, Nelson; Reyes Gómez, E.; Cavalcanti, S. B; Oliveira, L. E.
The propagation of light incident upon a 1D photonic superlattice consisting of successive stacking of alternate layers of a right-handed nondispersive material and a metamaterial, arranged to form a Cantor-like fractal, is considered. Plasmon-polariton excitations are thoroughly investigated within the transfer-matrix approach and shown to strongly depend on the Cantor step number N. More specifically, the number of plasmon-polariton bands corresponds to the number 2N− 1 of metamaterial layers within the unit cell.
Study of temperature and indium concentration-dependent dielectric constant and electron affinity effects on the exciton optical transition and binding energy in spherical GaSb–Ga1−xInxAsySb1−y–GaSb quantum dots
(2010-06) Sánchez Cano, R.; Porras Montenegro, Nelson
We have study the heavy-hole exciton states in GaSb–GaInAsSb–GaSb type-I spherical Quantum Dots, using temperature-dependent static dielectric constant and electron affinity, with a finite height potential barrier, as a function of the quantum dot radius for several values of Indium concentration. Our calculations have been worked out using interpolating methods to find the temperature and Indium concentration dependence of both the dielectric constant and electron affinity, in order to determine the conduction and valence band-offsets in GaSb–GaInAsSb–GaSb heterostructure by application of the Electron Affinity Rule. We have calculated the exciton binding energy and the corresponding transition energy from the exciton ground state to the heavy-hole level, using a variational procedure within the effective-mass approximation. We have found that the binding energy of the heavy-hole exciton presents changes due to the temperature dependence of the electron affinity and static dielectric constant. However, our results for the transition energy from the exciton ground state to the heavy-hole level coincide with those reported in a previous theoretical work, where we had found a very good agreement with photoluminescence and photoreflectance experimental studies at T=12 K in Ga1-xInxAsySb1-y films grown over GaSb substrates by liquid phase epitaxy
Study of transport and exitonic related optical phenomenain lowdimensional semiconductor structures.
(2004-03) Granada E., Juan Carlos; Porras Montenegro, Nelson; Calero Q., Jesús María; Universidad del Valle (Cali, Colombia); Física teórica del estado solido
In this project it is proposed to study the transport phenomena with in-plane applied magnetic fields in double barrier semiconductor heterostructures as well as the role of the channels offered by impurity states provided by well-on-center located impurities in this kind of structures Also we will study excited excitonic states in low dimensional semiconductor heterostructures, such as in quantum well-wires, quantum dots and in single and coupled double quantum wells. Special attention will be devoted to the study of the dependence of the excitonic binding energy with the size of the structure, with the interaction with doping impurities, with applied electric and magnetic fields. The calculation of the optical response due to excitonic states will be carefully studied. For the study of the transport properties in low-dimensional semiconductors we will employ the Green function technique developed by Keldysh for non-equilibrium systems. For the study of excited excitonic states in low dimensional semiconductor heterostructures we will use the effective mass approximation within the variational scheme and alternatively we will use the fractional dimension approach. We will compare our results with recent theoretical and experimental reports.
Temperature and hydrostatic pressure effects on the binding energy of magnetoexcitons bound to ionized-donor impurities in GaAs/AlxGa1−xAs quantum wells
(2011-04) Vivas Moreno, José Joaquin; Mejía Salazar, Jorge Ricardo; Porras Montenegro, Nelson
We have studied the quantum confinement, applied hydrostatic pressure, and temperature dependence of the binding energy of a magnetoexciton bound to a ionized-donor impurity in GaAs/Ga1−xAlxAs quantum wells, taking into account the spin-orbit coupling between the (Γv7,Γv8) and (Γc7,Γc8) multiplets, including the Al concentration, temperature, and applied hydrostatic pressure dependence on the electron effective-mass me(P,T,x) and the Landé ge(P,T,x) factor by using the well known five-level k · p theory. We have found that the binding energy Eb increases with the strong geometrical confinement, as well as with the growth-direction applied magnetic field. The presence of the ionized-donor impurity clearly increases the heavy-hole exciton binding energy. The quantum confinement, in part determined by the height of the barrier potential-well, i.e., by the Al concentration and the hydrostatic pressure, contributes to enhance the binding energy. Also, we found that the exciton binding energy increases with temperature due to the different temperature band-gap dependence of the well and barrier regions, which conduces to a net increasing of the potential barrier. Also, we have obtained a good agreement with previous theoretical and experimental findings. We hope the present work must be taken into account for the understanding of experimental reports and for the design of optoelectronic devices with multiple technological purposes.
Temperature and hydrostatic pressure effects on the photonic band structure of a 2D honeycomb lattice
(2010-02) Porras Montenegro, Nelson; Duque, C. A.
A standard plane-wave expansion method is used to investigate temperature and applied hydrostatic pressure dependence of the photonic band structure of a two-dimensional honeycomb lattice composed by cylindrical rods of GaAs, embedded in air. Present results suggest that for H-polarization an increment of hydrostatic pressure and temperature not only shifts the photonic band gaps, but diminish the energy width of the second and upper band gaps, while for E-polarization the first band gap is shifted to higher energies, without modifying the width of the other band-gaps, consequently modifying the tunability of this system.
Zero-(n) non-Bragg gap plasmon-polariton modes and omni-reflectance in 1D metamaterial photonic superlattices
(2011-05) Agudelo Arango, C.; Mejía Salazar, Jorge Ricardo; Porras Montenegro, Nelson; Reyes Gómez, E.; Oliveira, L. E.
A theoretical study of the photonic band structure and transmission spectra for 1D periodic superlattices with an elementary cell composed of two layers of refractive indices n(a) and n(b), which may take on positive as well as negative values, has been performed within the transfer-matrix approach. The dependence on the angle of incidence of the electromagnetic wave for excitation of plasmon-polaritons as well as the properties of the (n) = 0 gap were thoroughly investigated. Results are found for the generalized conditions that must be satisfied by the ratio a/b of the layer widths of metamaterial photonic superlattices, for both transverse electric and transverse magnetic polarizations, in order to have an omnidirectional (n) = 0 gap. The present study indicates new perspectives in the design and development of future optical devices.

Browsing by Author "Porras Montenegro, Nelson"

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