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Volume 01

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Nanopowders prepared by Solar Physical Vapor Deposition (SPVD)

The Solar Physical Vapor Deposition (SPVD) is an original process to prepare nanopowders. This method has been developed in Odeillo-Font Romeu in France using solar reactors working under concentrated sunlight in 2kW solar furnaces. Various oxides, pure or containing other elements in addition, have been obtained. This paper focus on ZnO and TiO2. based oxides It is shown that the X-Rays Diffraction analysis allows a fine nanostructural characterisation of the nanophases present in these nanopowders. In many cases, HRTEM or SEM and XPS complement the XRD analysis. The properties such as Electrical, magnetic properties, photoreactivity, luminescence … known on microstructured materials of the same composition are revisited on these nanopowders or on nanomaterials prepared from them and led in many cases to original behaviours.

Photovoltaic applications of Light Beam Induced Current technique

Light or Laser beam induced current technique (LBIC) is conventionally used to measure minority charge carrier’s diffusion
length LD by scanning a light spot away from collector (abrupt pn junction or Schottky contact). We show here the necessary
precautions to be taken in order to apply this method on materials used in photovoltaics. We talk about SRLBIC or spectral
response LBIC when this technique is combined with spectral reflectivity to allow determination of cells quantum efficiency.
From internal quantum efficiency analysis, one deduces an effective carrier diffusion length, Leff, including bulk and surface
recombinations. LBIC is, also, often used to reveal electrically active extended defects such as grain boundaries and dislocations,
and to check passivation efficiency of fabricated cells.

Reflexion/ Transmission of a plane wave on a plane interface

On a plane interface between two elastic half-space, P and SV waves propagating in the (x, z) pare related by Snell’s law and
the law of continuity of displacement components x u and z u and constraints zz σ and zx σ on both sides of the interface. An
incident wave P or wave SV generates two P or SV reflected waves and two transmitted waves P or SV. The four continuity
equations are written in the form of a matrix multiplied by a vector transmission-reflection coefficient, defined for potential
movement of the particles. For an planar boundary between fluids with different characteristic impedances, there is continuity of
z u and zz σ on both sides of the interface and the shear zx σ in the medium must vanish at the interface (fluid media involving
only perfect no viscosity, so that was normal stresses, not shear stress 0 xz σ = ). As soon as the angle of incidence exceeds a
critical value of incidence, the wave for which the value of incidence is greater than 30°
becomes evanescent. The reflectiontransmission
coefficients become complex.

Realization and study of ZnO thin films intended for optoelectronic

The objective of this study is the realization of zinc oxide (ZnO) thin films intended for optoelectronic applications. For this
purpose, thin films were prepared by spray pyrolysis technique from zinc acetate solutions of different molarities (0.025 M,
0.05 M and 0.1 M) used as precursors on Si and glass substrates heated between 200 and 500 °C. The nozzle to substrate
distance was varied between 20 and 30 cm. Structural, optical and electrical properties of the films have been studied. The
results indicated that the films deposited were transparent in the visible region, well adherent to the substrates and presented
surface roughness. All samples were polycrystalline in nature, having hexagonal würtzite type crystal structure. A (002)
preferred orientation was observed at 450°C and a 0.025M molarity. The optical energy gap measured was about 3.3 eV. The
refractive index values presented small variations with the deposition conditions and were located between 1.8 and 2.0. The
electrical properties showed that the samples are natively n-type semiconductor and the electrical conductivity at room
temperature varied between 10-5 and 102 (Ω.cm)-1.

Substrate effect temperature on Cu2ZnSnS4 thin films deposited by

Cu2ZnSnS4 (CZTS) thin films are a potential candidate for absorber layer in thin film solar cells. CZTS films were deposited by
spray ultrasonic technique. An aqueous solution composed of copper chloride, zinc acetate, tin chloride and thiourea like
precursors is sprayed on heated glass substrates at various temperatures. The substrate temperature was changed from 280°C to
360°C in order to investigate its influence on CZTS films properties. The DRX analyses indicated that Cu2ZnSnS4 films have
nanocrystalline structure with (112) preferential orientation and a crystalline size, ranged from 30 to 50 nm with increasing
substrate temperature. The obtained films are composed of SnS, ZnO, ZnS and Cu2ZnSnS4 phases. The optical films
characterization was carried by the measurement of UV-visible transmission. The optical gap was deduced from the absorption
spectra. Broad emissions at around 1.27 eV was observed in the photoluminescence spectrum measured at 77 K.

Investigation on chemical bath deposited CdS thin films

This paper presents the effect of solution temperature on optical, electrical and photoconducting properties of CdS films prepared by chemical deposition method. The solution temperatures used varied between 55 and 75 °C. X-ray diffraction
analysis showed that the prepared films have an hexagonal structure with (002) reflection. The transmittance data analysis showed a high transmission coefficient in visible range (85%) and an optical band gap lying between 2 and 2.4 eV. Scanning electron microscopy (SEM) and electrical measurements showed a pronounced effect of the solution temperature on thickness, dark conductivity and photoconductivity to dark conductivity ratio (σphot/σdark) parameters. The evolution of such parameters as a function of temperature are presented and discussed. It was found that the (σphot/σdark) ratio reaches high values of the order of 104 and 105 at 55 and 65 °C, respectively. These results indicate that CdS thin films prepared at these temperatures are convenient for optoelectronic and photovoltaic applications.

Elaboration and characterization of zinc oxide varistors

ZnO-based varistors were fabricated by sintering zinc oxide micro crystals with several additives of metal Oxides. The
effect of sintering temperature on varistor properties of (Bi, Co, Cr, Mn, Sb, Al)-doped ZnO ceramics was investigated in the range of 1280–1350 °C. The average grain size increased to 5.13 to 7.88 μm with the increase of sintering temperature. However,
the nonlinear coefficient of this system was nearly constant in the range of sintering temperature. The highest breakdown voltage was 1143.4 v / cm for the varistor sintered at 1350 °C the sample C sintered exhibited the best electrical properties.

Electronic structure calculation of the GaAs/AlAs quantum dot

Theoretical investigation of the electronic structure of GaAs/AlAs quantum dots superlattices is presented. We use the envelope function approximation in connection with Kronig-Penney model to calculate the conduction band structure of the cubic quantum dot crystal. . We show that, when quantum dots are separated by a finite barrier and positioned very close to each other so that there is a significant wave function overlap, the discrete energy levels split into three-dimensional minibands. We can control the electronic structure of this artificial quantum dot crystal by changing theirs technological parameters, the size of quantum dots, interdot distances, barrier height, and regimentation. This type of structure provides electronic and optical properties very important that are different to that of bulk and quantum well superlattices. The proposed engineering of three-dimensional minibands in quantum dot crystals allows one to fine-tune electronic and optical properties of such nanostructures.

Numerical analysis of GaAs MESFETs OPFET

A Tow dimensional numerical model of channel potential for GaAs MESFET (Metal semiconductor field effect transistor)doped uniformly .the model takes into acount the effects in channel region considering both the photoconductive effect and photovoltaic effect at the gate schottky . the 2-D potential distribution function in the active layer of the divice is solved numerically under dark and illumination condition.

Spin polarized transport in semiconductor

In this paper, we study two-dimensional spin polarized transport in semiconductors. Based on the some semiclassical considerations and taking account of the spin relaxation. We determined the relationship of the polarization as a function of
time and the distance. And we have also established the relationship of the drain current in a 2D channel of a transistor called « spin-FET » where it was matter to highlight this type of transport. This study was crowned with a numerical study of the characteristics of spinFET 2D transistor depending on the external field and internal characteristics of the semiconductor.

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