In this paper, we calculate the band gap and the band discontinuities of a GaN y AsBi x structure lattice matched to GaAs substrate using the conduction and the valence band anticrossing models at the same time. The results obtained show a good agreement with experiment. The nitrogen and the bismuth concentrations leading to a wavelength emission of 1.55 µm have been determined (x = 3.5%, y = 2%). This structure shows a good electron confinement resulting in a high characteristic temperature.Keywords GaNAsBi · Band anticrossing · Band offset · Band gap · Lattice matched IntroductionTemperature insensitive long wavelength (1.3 and 1.55 µm) laser diodes are very important sources for optical fiber communication. However, the conventional InP-based system exhibits a relatively low characteristic temperature due to poor electron confinement. As a novel GaAs-based material system, GaInNAs-based lasers grown on GaAs substrates offer a number of advantages in comparison with current GaInAsP-based lasers grown on InP substrates. The GaInNAs/GaAs system has a larger conduction band discontinuity and therefore provides better electron confinement and characteristic temperature (Henini 2005;Aissat et al. 2008;Ng et al. 2005). Moreover, this system is compatible with the well developed GaAs/AlAs distributed Bragg reflectors for surface emitting sources. Nowadays, the GaInNAs/GaAs lasers present very competitive characteristics at 1.3 µm wavelength, but it remains difficult to obtain comparable performance at longer emission wavelengths. Extending the wavelength of operation to 1.55 µm in this alloy system dictates N and In concentrations exceeding 2% and 35%, respectively, resulting in considerable degradation of the structural and optical properties. With increasing nitrogen concentration, the optical quality of the material usually deteriorates significantly resulting in a higher threshold current density of

Single and multiple InAs/InP strained quantum wells have been grown by hydride vapor-phase epitaxy (HVPE). A compact set of vent/run valves monitored by manifold switches and a computer allowed the vapor species to be changed. InAs growth times of 4–24 s followed by etching times of 7–14 s, in an InCl, HCl, and H2 atmosphere, were used to control the thickness and interface abruptness. Low-temperature photoluminescence (PL) spectra have revealed emissions either in the form of a single peak or well-resolved multiple peaks attributed to monolayer variation in quantum-well thickness. The thinnest well obtained, observed for the first time by HVPE, has a PL energy transition at 1.28 eV. Experimental data agree well with theoretical calculations, taking into account strain effects on band structure and effective masses. The full widths at half maximum indicate good interfacial abruptness.

Substrate dipping in a composite sol-gel solution was used to prepare smooth and rough thin films of titanium dioxides (TiO2) on porous silicon (PS) and conductor glass. The fabrication process and optical measurements of these layers are presented. Sol-gel films were coated by dip-coating method on porous silicon layer. The characterizations of deposited layer were performed by spectral response, ellipsometry and spectrophotometry. The results show that the optical and electrical properties of the structures strongly depend on the deposition conditions of TiO2. In addition, the band gap energy Eg and refractive index of the structure can be easily varied depending on TiO2 thicknesses and calcination temperatures. Finally, the electrical and optical parameters show a promising result in solar cells application and photocatalytic activity.

This text deals with the study of the characteristics of GADC filters by taking into account the dispersion. After having defined the characteristics of the filter, the influence of separation between the guides and filter length on the characteristics of the filter are studied. It is shown that dispersion plays a very important role in the evaluation of spectral features of the filter and can not be neglected.