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International Journal of Modern Physics B

Effect of size distribution on the optical properties of quantum wire systems

Reza Khordad, Hossein Bahramiyan

Published Apr 25, 2014• 10 citations
Publisher

Abstract

In this paper, we have studied optical properties of an inhomogeneous quantum wire system. In this regard, we have calculated the absorption coefficients and refractive index changes using density matrix method. We have investigated the effect of size variation on these optical properties. The wires are considered to be triangle with infinite potential at the boundaries. We have described the size nonuniformity distribution by a Gaussian function. It is shown that the optical properties of the quantum wires depend strongly on the wire size distribution described by the parameters a0 and D (the average side length and standard deviation of quantum wire, respectively). It is deduced that the effect of size distribution on the optical properties of triangle quantum wire is noticeable.

DOI
10.1142/s0217979214501197

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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.
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.
Optical properties of quantum well nanostructure for typical GaAs/AlxGa1-xAs are investigated in a new approach. By using the point canonical transformation method and numerical solution of the Schrödinger equation, the energy levels and wave functions of electrons in the quantum well confinement potential are calculated. Then, the effect of position-dependent effective mass on the intersubband optical absorption coefficient and the refractive index changes of the quantum well calculated by compact density matrix method, are studied. Results are compared with the case of constant mass. Our results show that with considering spatially varying electron effective mass linear and nonlinear optical properties increases and shifts toward the lower energies. Researches on this matter open a new field in fundamental and applied physics, and also offer a wide range of potential applications for photonic devices.
The effect of geometrical anisotropy is numerically investigated on the linear and nonlinear optical refractive index changes of a GaAs quantum dot which is located at the center of a Ga1-xAlxAs cylindrical nano-wire. The finite difference approximation has been used for obtaining energy eigenvalues and corresponding wave functions. Also, the compact density matrix formalism is applied to investigate linear, third order nonlinear and total optical refractive index (RI) changes. The optical properties are calculated as a function of the incident photon energy for different ellipsoid aspect ratio and dot radius. The results clearly reveal that the dot anisotropy plays an important role in determining the magnitude of nonlinear RI changes which enable us to adjust saturation condition. We also found that the dot anisotropy shifts optical spectrum towards both lower and higher energies which depend on the shape of dot (spherical, prolate or oblate quantum dot) and dot radius.