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Progress In Electromagnetics Research M

LINEAR AND NONLINEAR REFRACTIVE INDEX CHANGES IN SPHERICAL QUANTUM DOT

Bekir Çakır, Yusuf Yakar, Ayhan Özmen

Published Jan 1, 2011• 13 citations
Publisher

Abstract

In this study, refractive index changes associated with in- tersubband transitions in a spherical quantum dot, GaAs/AlxGa1ixAs, have been theoretically calculated in the presence of impurity. In this regard, the efiect of dot radius, stoichiometric ratio, impurity and in- cident optical intensity on the refractive index changes have been in- vestigated for the transitions between higher energy states, i.e., 1s-1p, 1p-1d and 1d-1f. The results show that these parameters have a great in∞uence on the refractive index changes.

DOI
10.2528/pierm11080903

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In this study, refractive index changes associated with in- tersubband transitions in a spherical quantum dot, GaAs/AlxGa1ixAs, have been theoretically calculated in the presence of impurity. In this regard, the efiect of dot radius, stoichiometric ratio, impurity and in- cident optical intensity on the refractive index changes have been in- vestigated for the transitions between higher energy states, i.e., 1s-1p, 1p-1d and 1d-1f. The results show that these parameters have a great in∞uence on the refractive index changes.
Intersubband optical absorption coefficient and refractive index changes of a weakly prolate ellipsoidal quantum dot, using the compact-density matrix formalism and iterative method, are investigated. In this regard, the linear and nonlinear intersubband optical absorption coefficient and refractive index changes of a GaAs / Al x Ga 1-x As ellipsoidal quantum dot, as functions of the dot radius, ellipticity constant, stoichiometric ratio and incident light intensity are calculated. The results indicate that absorption coefficient and refractive index changes strongly depend on the light intensity, size and geometry of the dot and structure parameters such as aluminium concentration in GaAs / Al x Ga 1-x As structures.
Simultaneous effects of an on-center hydrogenic impurity and band edge non-parabolicity on intersubband optical absorption coefficients and refractive index changes of a typical GaAs/Al x Ga 1−x As spherical quantum dot are theoretically investigated, using the Luttinger—Kohn effective mass equation. So, electronic structure and optical properties of the system are studied by means of the matrix diagonalization technique and compact density matrix approach, respectively. Finally, effects of an impurity, band edge non-parabolicity, incident light intensity and the dot size on the linear, the third-order nonlinear and the total optical absorption coefficients and refractive index changes are investigated. Our results indicate that, the magnitudes of these optical quantities increase and their peaks shift to higher energies as the influences of the impurity and the band edge non-parabolicity are considered. Moreover, incident light intensity and the dot size have considerable effects on the optical absorption coefficients and refractive index changes.
Linear, nonlinear, and total refractive index changes are investigated theoretically in asymmetric coupled quantum wells. The analytical expressions for the linear and third-order nonlinear refractive index changes are obtained based on the density matrix method and the iterative approach. Numerical calculations are performed for typical GaAs/Al(subscript x)Ga(subscript 1-x)As asymmetric coupled quantum wells. The calculated results reveal that a large variation of the refractive index near the transition energy can be obtained in asymmetric coupled quantum wells, and that the incident optical intensity and the structure parameters, such as the barrier width and the right-well width, have great effects on the total refractive index changes.
In the current study, linear, nonlinear and total relative refractive index changes of a single shallow hydrogenic donor atom confined in semiconductor core/shell/shell quantum dot heterostructure are investigated in detail by compact density matrix formalism. For this purpose, the energy eigenvalues and the corresponding wave functions are calculated by diagonalization method in the effective mass approximation. Then, intersubband 1s→1p and 1p→1d donor transition energies are calculated. In the study, the effects of core/shell sizes, donor position and depth of confinement potential are analyzed. The numerical results show that the linear and nonlinear refractive index changes undergo significant changes.
The study presents results of the linear and non-linear optical properties of GaAs quantum dots. The reported work aims to provide new results of the quantum dot optical properties confined in Hua plus modified Eckart (HPME) potential. To obtain analytical expressions for the energy eigenvalues and the wave functions, we solved the time-independent Schrödinger equation for the HPME potential by using the parametric Nikiforov-Uvarov (NU) method. Investigation of the linear, third-order nonlinear, and total absorption coefficients and refractive index changes was done with the help of the density matrix approach. The results showed that the energy decreases in a linear manner as the potential parameter, V0. Also, it is observed that as the barrier slope increases, the peaks of the linear, third-order linear, and total absorption coefficient tend to higher values of energy. Furthermore, as the barrier slope increases, the change in refractive indices increases, and their positions shift to higher energies. Additionally, an increase in the structure parameters and optical intensity greatly influences the absorption coefficients and the refractive index changes of the quantum dots.
The linear and third-order nonlinear optical absorption coefficients (ACs) and the refractive index change (RIC) for a spherical quantum dot, having a hydrogenic impurity under an applied magnetic field have been theoretically studied. In numerical calculations, a variational scheme is adopted within effective mass approximation to determine the energy eigenvalues for the impurtiy. The variations of impurity binding energy with the dot radius, the linear and nonlinear ACs and RIC with the photon energy are investigated and effect of homogeneous magnetic field strength is discussed on these optical properties. It has been found that the binding energy, ACs and RIC are sensitively dependent on the magnetic field strength. Moreover, the calculated results also indicate that the absorption peak energies move to higher energies with increasing magnetic field.