25 research outputs found
High Second-Order Nonlinear Susceptibility Induced in GaN/AlxGa1 – xN Coupled Quantum Well for Infrared Photodectors Application
The second harmonic generation (SHG) of GaAs/AlxGa1 − xAs a wurtzite coupled quantum wells (CQWs)
is studied theoretically for different widths of well, barrier and values Al concentration, taking into account
the strain-induced piezoelectric (PZ) effects. The analytical expression of the SHG susceptibility is deduced
by using the compact density matrix approach. The confined wave functions and energies of electrons
GaN/AlxGA1 – x N are calculated in the effective-mass approximation, solving the Schrödinger equation by
Numerov’s method using six order approximations for the derivatives. The calculated results also reveal
that by adjusting the widths of well, the barrier and Al concentration respectively, a set of optimal structural
parameters can be found for obtaining a strong SHG susceptibility.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2777
Absorption Coefficients of GaN / AlxGa1 – xN Core-Shell Spherical Quantum Dot
The total absorption coefficient in spherical GaN/AlxGa1 – xN core-shell nanodots is theoretically investigated taking into account effective mass approximation. The influence of the nanosystem geometry upon the energy spectrum and transition energy δE associated to interlevel transitions is studied. We found that the energy transitions vary with the core-shell radius, and the peak position of the total absorption coefficient is greatly affected by changing of the shell radius. The possibility of tuning the resonant energies by using the geometric core shell effect of the spatial confinement can be useful in the optoelectronic devices applications. Also we observed that the magnitudes of the total absorption coefficient can be increased significatly compared traditional cases of QD, and the peaks are shifted to the lower energies.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2960
Modélisation des propriétés diélectriques des nanocomposites
Dans ce travail, nous nous intéressons aux propriétés diélectriques dans le domaine des micro-ondes (2.45, 9.50 et 35 GHz) des composites constitués des inclusions de noir de carbone dans une matrice résine époxyde. Nous avons utilisé deux types de carbone : le monarch 700 et le sterling, dont les diamètres des inclusions sont respectivement 0.018 et 0.175 μm. Les résultats obtenus montrent que la taille des particules conductrices parait être un paramètre prépondérant pour définir la permittivité complexe de ces composites. Il résulte de cette étude que les modèles proposés pour la détermination de permittivité de ces milieux, devront nécessairement prendre en considération la taille des inclusions.Mots-clés : Lois de mélange, propriétés diélectriques, permittivité complexe,nanocomposites, matrice époxyde, inclusions de carbone
Schottky Diodes and Thin Films Based on Copolymer: Poly(aniline-co-toluidine)
Poly(aniline-co-o-toluidine) (PANI-co-POT) thin films were deposited on indium tin oxide- (ITO-) coated glass substrates by electrochemical polymerization under cyclic voltammetric conditions from aniline-co-o-toluidine monomer in an aqueous solution of HCl as a supporting electrolyte. These measurements showed that the optical band gap of the copolymer films is on the order of 2.65 eV. On the other hand, ITO/PANI-co-POT/Al devices were fabricated by thermal evaporation of Aluminum circular electrodes on the as-deposited PANI-co-POT films. The Current-Voltage characteristics of these devices are nonlinear. The diode parameters were calculated from I-V characteristics using the modified Shockley equation. The C-F characteristics were also measured
Dielectric Behavior of Ceramic (BST)/Epoxy Thick Films
Composite materials were made by mixing powders of Ba1−xSrxTiO3 (x=0.2 and 0.4) ceramics and epoxy resin with various volume fractions (vol%). Dielectric measurements of these composites were performed as a function of filler ratio in the range 100–360°K at 10 KHz. The dielectric constant of the composite increased with increasing volume fraction varies slightly with temperature. The 20 vol% of BST(0.4)-epoxy composite had the highest dielectric constant of 19.4 and dielectric loss tangent of 0.027. Among the dielectric mixing models presented, the model of Lichtenecker shows the best fit to the experimental data for both composites
Structural, Optical and Electrochromic Properties of Nanocrystalline TiO
Nanocrystalline TiO2 thin filmswere prepared by spin coating on covered glass substrates with an indium tin oxide (ITO) layer. The structural, electrochromic and optical properties of the films were investigated. The films are crystallized predominantly in the anatase phase with lattice parameters a = b = 0.378 nm and c = 0.958 nm . The crystallite size was found to be of the order of 14 nm. The films showed reversible coloration/bleaching cycles as demonstrated by cyclic voltametry and current–time transients. The transmission of the blue colored films decreased and their
absorption edge was less sharp and shifted to higher wavelengths as a result of the intercalation of Li+
ions
Theoretical Analysis of Optical Gain in GaN / AlxGa1 – x N Quantum Well Lasers
In this study, we investigated numerically the effect of aluminum concentration, temperature and well
width on optical gain GaN / AlxGa1 – xN quantum well lasers, taken into account effective mass approximation.
The numerical results clearly show that the increasing of well width, and decreasing of temperature and
Aluminum concentration, the optical gain increases
Electro-optic effect in GaN/Al₀.₁₅Ga₀.₈₅N single quantum wells for optical switch
he second-harmonic generation (SHG) susceptibility of wurtzite type gallium
nitride with single quantum wells has been theoretically investigated in the framework of
the compact-density-matrix approach. The confined wave functions and energies of
electrons in GaN/AlxGa₁₋xN have been calculated in the effective-mass approximation,
solving the Schrödinger equation by Numerov’s method using the second and fourth
order approximations for the derivatives. The numerical results for typical
GaN/Al₀.₁₅Ga₀.₈₅N quantum wells show that a strong SHG effect can be realized in
electric field by choosing some optimized structural parameters