Physique
Synthesis, characterization and structural study of perovskite ceramics for piezoelectric applications
In this work we have prepared lead-free ceramics BaTiO3, CaTiO3 and Ba0.85Ca0.15Ti0.9Zr0.1O3 successfully from different raw materials barium carbonate (BaCO3) calcium carbonate (CaCO3) dioxide of titanium (TiO2) and zirconium dioxide (ZrO2) by the conventional solid state reaction technique at different sintering temperatures. These materials are mixed for 6 hours and sintered at temperatures of 1200 °C to 1300 °C for 2 hours. The sintering temperature has been varied to study its effects on microstructure and structural properties. Structural parameters were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM). Differential thermal analysis coupled with thermogravimetric analysis (ATG-ATD) was performed mainly to follow the process of precursor decomposition and formation of the perovskite phase. The XRD analysis results clearly show the synthesis of the perovskite phase as well as highlighting the formation of the Ba2TiO4 phase in addition to the BaTiO3 phase. The diffractogram obtained shows that the BCTZ symmetry is both Cubic with a space group Pm-3m and orthorhombic with a space group R3m. The calculated phase rates are: 10% and 90% respectively. Voir les détails
Mots clés : Lead free ceramics, synthesis, microstructure, Perovskite
Modeling and simulation of In0.15 Ga0.85 N/GaN strainquantum well structure for solar cells application
Quantum well solar cells based on III-V nitride semiconductor materials are a great technological interest by means to their physical and optical properties. In this study the effect of quantum well number on the characteristics (J-V), (P-V) and efficiency for the structure GaN/In 0.15 Ga0.85 N/ GaN was studied. our result showed that, the increase in the number of wells is accompanied by the increase of the light current density and the efficiency, for example with 50 wells we found Jight = 14(mA /cm2) and a efficiency 28%. Voir les détails
Mots clés : Quantum well, solar cell, GaN, InGaN
Melt Surface Temperature Monitoring In Tiltable Induction Furnace
The supervision of the induction furnace is the subject of increasing development because of the rising demand on reliability and safety. An essential aspect of the pyrometers of induction furnace is the determination of the exact temperature on the melt surface related to the current and frequency flow resulting from optimum coil position depending on the applied actual power. With the aid of the mathematical model that describes the appearance and development of the temperature change in the area of inductive cold wall crucible melting, with the use of the automatic control methods it is possible to determine the change of temperature variation corresponding to direct visualization of a meniscus forms on the melt surface under the energy created by the induction coil, the latter can fully or partly influence the meniscus. To solve the problem of pyrometer temperature variation we propose the determination and the study of the total interaction force related to the operating current of the induction generator. This contribution presents an application for melt temperature change detection through a case study of the tiltable induction furnace with induction generator MFG-20. The study indicates that the pyrometer of the measurement temperature is powerful device related to the development of a new control method. Voir les détails
Mots clés : Tiltable induction Furnace, cold wall crucible melting, pyrometer measurements, Infrared thermography measurement.
Propriétés Optique de TiO2 et Application de la Méthode de Swanepoel pour la Détermination de l’Épaisseur Optique et de l’Indice de Réfraction
Dans ce travail, des nano-films de dioxyde de titane « TiO2 » ont été déposés par pulvérisation cathodique en utilisant une cible en céramique de Ti pur de 3" de diamètre et 0,250" d'épaisseur avec une pureté de 99,99% sur des substrats en verre à des épaisseurs (e) différents. Nous visons par ce travail d’étudier l’effet de l’épaisseur sur les propriétés optiques de TiO2 nano films. Pour cela, nous avons utilisé la spectroscopie de transmittance optique UV-Visible pour la caractérisation optique. La variation du gap optique des films est inversement proportionnelle à la variation de l’épaisseur de 3,6 eV à 3,8 eV, respectivement. Pour la détermination de l'indice de réfraction et l'épaisseur du film nous avons utilisé la méthode proposée par Swanepoel, qui s’articule sur l’utilisation des franges d’interférence. On observe que, l'indice de réfraction n augmente avec l’augmentation de l'épaisseur de la couche déposée. Voir les détails
Mots clés : couches minces, pulvérisation, semi-conducteur, TiO2, nano-films, UV-Vis, épaisseur, indice de réfraction, Swanepoel.
Numerical simulation study of a high efficient AlGaN-based ultraviolet photodetector
In this paper, a two-dimensional (2D) numerical simulation study of a p+-n-n+ AlGaN-based ultraviolet (UV) photodetector, which is designed to achieve true solar blindness with a cutoff wavelength of 0.31 µm, is presented. The device performance is evaluated by investigating both the current density-voltage characteristics and the spectral response (SR). The proposed structure is optimized in terms of the fundamental geometrical and doping parameters. During the simulations, it was found that the detector is sensitive to the UV rays in the 0.155-0.37 µm wavelength range and the spectral response can reach 0.156 AW-1 under a light intensity of 1 Wcm-2 at zero-bias voltage and room temperature. This SR peak value increases further under reverse bias conditions. The temperature effect on the detector SR and the impact of an explicit trap concentration located into the p+ and n-region are also investigated. The spectral response decreases for a temperature exceeding 420 K. At the same time, the SR reference values begin to be affected only for acceptor and donor trap densities that are much higher than the local (total) doping concentration. Voir les détails
Mots clés : AlGaN, Numerical simulation, Photodetector, Spectral response, Trap Density
Elaboration et caractérisation des dépôts Aluminium sur Silicium(Al/Si(400))
Dans ce travail nous nous sommes intéressés à la croissance et la diffusion superficielle de l’Aluminium sur un substrat de Silicium (400). Ce travail comporte deux parties :Le première partie consiste à réaliser sous-vide et à température ambiante des dépôts de différentes épaisseurs d = 240, 510, 720, 870 et 1050 A°. Ces dépôts ont été analysés quantitativement par DRX. L’Aluminium semble croisse sur le silicium selon le mode de Frank-van Der Merwe.La deuxième partie de notre travail est consacrée à l’étude de l’effet de la température de recuit sur la morphologie des dépôts réalisés à température ambiante. Les températures de recuits sont : 100,150, 200, 250, 300, 350 et 400C°. d’après les résultats d’analyse par DRX des dépôts traités, les îlots (2D) d’Aluminium formés à température ambiante se transforment en augmentant la température de recuit, en îlots (3D) plus hauts et plus ramenés. Voir les détails
Mots clés : Évaporation thermique, Silicium, Aluminium, diffusion, DRX.
SnS Thin Films Prepared by Chemical Spray Pyrolysis method
Tin sulfide (SnS) is interesting semiconductor that found application is several fields such as photovoltaic and gas sensor due to its interesting optical and electrical properties. In the present study, chemical spray pyrolysis deposition (CSP) was used to deposit tin sulfide (SnS) thin films onto glass substrates at 350°C. The starting solutions were prepared by the dilution of SnCl2 and thiourea in distilled water. The structural, optical and electrical, properties of the films were determined using X-ray diffraction, UV visible transmittance and Hall Effect measurements respectively. The influences of flow rate (10, 15 and 20 ml/h) in the structural, optical and electrical properties were determined. The XRD data confirms that the films prepared at low flow rate are a mixture of SnS and Sn2S3 phases. However, when the flow rate is increase; structures of the films are amorphous. From the UV-visible transmittance in the visible range we noticed that films optical band gap value ranged from 1.2 to 1.5 eV. The Hall Effect measurements indicate that SnS thin film exhibits p-type conduction with a conductivity decrease by two orders from 5.15x10-3 to 5.8x10-7 (?.cm)-1. Voir les détails
Mots clés : tin sulfide; solar cell; UV-visible, spary pyrolysis.
Electrical Characteristics of SnS /ZnS Heterojunction
Thin sulphide (SnS) is a promising candidate for a low cost, no toxic solar cells absorber layer. In this paper thin films of SnS were prepared by spray pyrolysis onto glass and ZnS/FTO coated glass substrates at different substrate temperatures in the range 250-400°C. SnS were characterized with X-rays diffraction and scanning electron microscopy and UV visible transmittance. The electrical properties of SnS/ZnS heterojunctions were determined using recording their current-voltage I(V) and capacitance-voltage (C-V) characteristics at ambient and at different measurement temperatures from 28-94°C. The results analysis indicate that the saturation current varied from 0.68 to 2.8 µA and series resistance from 191 to 800 ? , The structures ideality factor is ranged from 1.37 to 2.7. The diffusion potential (Vd) was determined by the intercept of extrapolation of 1/C2-V curve to the abscise axis (V=0) we found Vd values ranged from 0.67 to 1.2 V. Voir les détails
Mots clés : Tin sulfide; thin films; solar cell; spray pyrolysis; SnS/CdS Heterojuction.
Structural, Optical and Electrical Properties of PbS Thin Films Deposited by CBD at Different Bath pH
PbS thin films were grown on glass substrates by chemical bath deposition (CBD). The precursor aqueous bath contained 1mole of lead nitrate, 1mole of Thiourea and complexing agents (triethanolamine (TEA) and NaOH). Bath temperature and deposition time were fixed at 60°C and 3 hours, respectively. However, the PH of bath was varied from 10.5 to 12.5. Structural properties of the deposited films were characterized by X-ray diffraction and Raman spectroscopy. The preferred direction was revealed to be along (111) and the PbS crystal structure was confirmed. Strains and grains sizes were also calculated. Optical studies showed that films thicknesses do not exceed 600nm. Energy band gap values of films decreases with increase in pH and reached a value ~ 0.4eV at pH equal 12.5. The small value of the energy band gap makes PbS one of the most interesting candidate for solar energy conversion near the infrared ray Voir les détails
Mots clés : CBD, PbS, pH, Thin films, X-ray diffraction
The effect of copper concentration on CdS/CZTSheterojunction properties
Cu2ZnSnS4 (CZTS) / CdS heterojunctions have been prepared by a successive deposition of CZTS and CdS thin films on glass substrates by spray pyrolysis and chemical bath deposition techniques respectively. The concentration of cupric chloride in the starting solution has been varied in order to investigate its influence on device properties. The realized CZTS/CdS heterojunctions were characterized by recording their IV characteristics at ambient and at different temperatures. The current-voltage (IV) characteristics of the different heterostructures exhibit a rectifying behavior with a good ideality factor ranged from 1.5 to 2.7. From these IV characteristics we have deduced the saturation current series resistance and barrier height of the devices. We found that these quantities vary from 0.22 to 1.68µA for the saturation current and from 300 to 2500 for the series resistance. We have deduced also that the potential barrier was found between 0.3 and 1.31eV. From these results we inferred that the realized structures are suitable for their applications as solar cells. Voir les détails
Mots clés : CZTS; heterojunction; spray pyrolysis; solar cells;IV