Propiedades ópticas no lineales en anillos cuánticos de GaAs

RESUMEN: Se estudian los efectos de la presión hidrostática, de un campo eléctrico externo y de la concentración de aluminio en anillos cuánticos de GaAs con diferentes geometrías sobre los niveles de energía del electrón y de las energías de enlace de una impureza donadora poco profunda. Además se calculan la absorción óptica intra-banda de orden lineal y no lineal y los cambios relativos del índice de refracción, se utiliza el método variacional y las aproximaciones de masa efectiva y de bandas parabólicas. Para los cálculos de las propiedades 'ópticas no lineales se han utilizado el método de la matriz densidad compacto y un método iterativo. Las energías de los estados 1s y 2s se calculan como una función de las geometrías de los anillos, la posición de la impureza y los agentes externos. Para la absorción óptica intra-banda y los cambios relativos del índice de refracción asociados con las transiciones entre el estado base y la primer estado excitado, se investigó su dependencia con la energía del fotón incidente, con diferentes valores de los agentes externos y la posición de la impureza. Los resultados muestran que la energía de enlace se comporta como una función creciente/decreciente de los radios interno/externo y de la presión hidrostática, el campo eléctrico y de la concentración de aluminio. En el caso de los coeficientes de absorción óptica intra-banda los resultados muestran un desplazamiento al azul y, o un desplazamiento hacia el rojo de los picos máximos que puede ser inducido como resultado de las influencias planteadas: La geometría del anillo cuántico correspondiente, la posición de la impureza y la presión hidrostático, el campo eléctrico y la concentración de aluminio

Linear and nonlinear optical absorption coefficients in GaAs/Ga1−xAlxAs concentric double quantum rings : Effects of hydrostatic pressure and aluminum concentration

ABSTRACT: The linear and nonlinear intra-band optical absorption coefficients in GaAs/Ga1−xAlxAs two-dimensional concentric double quantum rings are investigated. Taking into account the combined effects of hydrostatic pressure and aluminum concentration the energies of the ground and the first excited state have been found using the effective mass approximation and the transfer matrix formalism. The energies of these states and the corresponding threshold energy of the intra-band optical transitions are examined as a function of hydrostatic pressure and aluminum concentration for different sizes of the structure. We also investigated the dependencies of the linear, nonlinear, and total optical absorption coefficients as functions of the incident photon energy for different values of hydrostatic pressure, aluminum concentration, sizes of the structure, and incident optical intensity. Its is found that the effects of the hydrostatic pressure and the aluminum concentration lead to a shifting of the resonant peaks of the intra-band optical spectrum

Electron Raman scattering in pyramidal quantum dots

ABSTRACT: The Raman scattering related with electrons in pyramidal quantum dots is theoretically investigated. The electron Raman differential cross section is calculated making use of analytically determined quantum states within the effective mass approximation. The features of the Raman differential cross section are discussed in terms of their dependence on the changes of the quantum dot geometry.RESUMEN: En este artículo se investiga teóricamente la dispersión Raman de electrones en puntos cuánticos piramidales. Se reporta la sección transversal diferencial Raman electrónica usando los estados cuánticos determinados analíticamente dentro de la aproximación de masa efectiva. Las características de la sección transversal diferencial Raman se discuten en términos de su dependencia de los cambios de la geometría de punto cuántico

Outer-shell photodetachment of the metastable Mg− [core]3s3p2 and Ca− [core]4s4p2 4Pe states

ABSTRACT: We report on calculated outer-shell photodetachment cross sections from the metastable (core)nsnp2 4Pe states in Mg− (n=3) and Ca− (n=4) negative ions in the photon energy range w=0–10 eV. Double-ionization thresholds for Mg II and Ca II as well as doubly excited thresholds of the residual atoms Mg I and Ca I are located within the photon energy range considered and thus doubly and triply excited states of both Mg− and Ca− are reached. We use a complex scaled configuration interaction (CSCI) method for the three active electrons supplemented with a sophisticated model potential as developed by Laughlin (Phys. Scr. 45, 238 (1992)) to account for core-valence interactions. The CI calculations are based on Mg+ and Ca+ one-electron orbitals expanded in terms of B-spline basis set. We compare our cross sections with the only calculation available up to a photon energy 0.25 Ry (w~3.4 eV) (Zeng et al., Phys. Rev. A 62, 022713(2000)) performed by using the R-matrix method, in which only one 4Po resonance for Mg− and two (4Po and 4Do) for Ca− were predicted. In this work, by analyzing both the cross sections and the locations of the S-matrix poles in the complex plane, we are able to predict six 4Po, four 4Do, and four 4So resonant states for Mg−, and three 4Po and two 4Do resonant states in Ca−

Impurity-Related Nonlinear Optical Absorption in Delta-Doped Quantum Rings

Using a variational procedure within the efective mass approximation, we have calculated the hydrogenic impurity binding energy as well as the impurity-related nonlinear optical absorption in a single quantum ring with axia ln-type delta-doping

Donor impurity-related linear and nonlinear intraband optical absorption coefficients in quantum ring : effects of applied electric field and hydrostatic pressure

ABSTRACT: The linear and nonlinear intraband optical absorption coefficients in GaAs three-dimensional single quantum rings are investigated. Taking into account the combined effects of hydrostatic pressure and electric field, applied along the growth direction of the heterostructure, the energies of the ground and first excited states of a donor impurity have been found using the effective mass approximation and a variational method. The energies of these states are examined as functions of the dimensions of the structure, electric field, and hydrostatic pressure. We have also investigated the dependencies of the linear, nonlinear, and total optical absorption coefficients as a function of incident photon energy for several configurations of the system. It is found that the variation of distinct sizes of the structure leads to either a redshift and/or a blueshift of the resonant peaks of the intraband optical spectrum. In Maddition, we have found that the application of an electric field leads to a redshift, whereas the influence of hydrostatic pressure leads to a blueshift (in the case of on-ring-center donor impurity position) of the resonant peaks of the intraband optical spectrum

Donor impurity-related optical absorption in GaAs elliptic-shaped quantum dots

ABSTRACT: The conduction band and electron-donor impurity states in elliptic-shaped GaAs quantum dots under the effect of an externally applied electric field are calculated within the effective mass and adiabatic approximations using two different numerical approaches: a spectral scheme and the finite element method. The resulting energies and wave functions become the basic information needed to evaluate the interstate optical absorption in the system, which is reported as a function of the geometry, the electric field strength, and the temperature

Pyramidal core-shell quantum dot under applied electric and magnetic fields

We have theoretically investigated the electronic states in a core/shell pyramidal quantum dot with GaAs core embedded in AlGaAs matrix. This system has a quite similar recent experimental realization through a cone/shell structure [Phys. Status Solidi-RRL 13, 1800245 (2018)]. The research has been performed within the efective mass approximation taking into account position-dependent efective masses and the presence of external electric and magnetic felds. For the numerical solution of the resulting three-dimensional partial diferential equation we have used a fnite element method. A detailed study of the conduction band states wave functions and their associated energy levels is presented, with the analysis of the efect of the geometry and the external probes. The calculation of the non-permanent electric polarization via the of-diagonal intraband dipole moment matrix elements allows to consider the related optical response by evaluating the coefcients of light absorption and relative refractive index changes, under diferent applied magnetic feld confgurations

Editorial

La Revista EIA se complace en rendir un homenaje al Dr. Gabriel Poveda Ramos, Ingeniero Químico, Ingeniero Electricista, Matemático y Doctor en Ingeniería.La Revista EIA se complace en rendir un homenaje al Dr. Gabriel Poveda Ramos, Ingeniero Químico, Ingeniero Electricista, Matemático y Doctor en Ingeniería

Editorial

La ciencia silenciosa¿Y qué pasaría si los seres humanos no fuésemos curiosos y no buscáramos el conocimiento? ¿Podemos vivir sin la ciencia? ¿De verdad podríamos existir como especie sin la ciencia? Los demás seres vivos del planeta lo han hecho y lo harán, pero nosotros no.La ciencia silenciosa¿Y qué pasaría si los seres humanos no fuésemos curiosos y no buscáramos el conocimiento? ¿Podemos vivir sin la ciencia? ¿De verdad podríamos existir como especie sin la ciencia? Los demás seres vivos del planeta lo han hecho y lo harán, pero nosotros no