Mixing of Au in Si induced by secondary and high-order recoil implantation

The mixing of Au in Si induced by secondary and high-order recoil implantation was investigated using 350 keV Ar + and 350 keV Kr + ions to fluences from 1?×?10 16 to 3?×?10 16 ions/cm 2 at room temperature. The thickness of the Au layer evaporated on Si substrate was ~2400 .The ranges of the Ar and Kr ions were chosen to be lower than the thickness of the Au layer in order to avoid the ballistic mixing produced by the primary knock-on atoms. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the effects induced by Ar and Kr irradiation at the interface of Au-Si system. We observed that in the case of the irradiation with Ar + ions, a broadening of the Au-Si interface occurred only at the fluence of 3?×?10 16 Ar + /cm 2 and it is attributed to the surface roughening induced by ion bombardment. In contrast, the RBS analysis of a sample irradiated with 2?×?10 16 Kr + /cm 2 clearly showed, in addition to the broadening effect, the formation of a mixed zone of Au and Si atoms at the interface. The mixing of Au in Si atoms can be explained by the secondary and high-order recoil implantation followed by subsequent collision cascade

The influence of hopping on modulated photoconductivity

ID = 432International audienc

LA DEPENDANCE EN TEMPERATURE DE LA PHOTOCONDUCTIVITE A L’ETAT STATIONNAIRE BASEE SUR LE MODELE "DEFECT POOL" DANS LE SILICIUM AMORPHE HYDROGENE (a-Si:H) INTRINSEQUE ET DOPE.

Ce travail est une étude par simulation numérique de la photoconductivité à l'état stationnaire ( σp) en fonction de latempérature (T) dans le a-Si:H intrinsèque, dopé de type (n) et dopé de type (p). La densité des états (DOS) du matériau estformée par des queues de bande de valence (QBV) et de conduction (QBC) de formes exponentielles et une distribution de ladensité des états des liaisons pendantes (LP) calculée à partir du modèle "defect pool" (MDP) en partant des réactionsd’équilibre chimique qui décrivent le mécanisme de conversion des liaisons faibles SiSi en LP. Les transitions électroniquesrelatives aux états des QB sont décrites par les statistiques de Simmons–Taylor tan disque celles des LP sont décrites par desfonctions d’occupation propres aux LP. La dépendance de la photoconductivité à l'état stationnaire de la température basée surle MDP ainsi simulée pour différents degrés de dopage est comparée à celle observée expérimentalement. On vérifie que leMDP constitue le modèle théorique le plus adéquat vis a vis des résultats expérimentaux. Les allures des courbes simulées sonten bon accord avec celles observées expérimentalement. A savoir la région de " thermal quenching" à hautes températuressuivie d’une région faiblement activée à moyennes températures. L’interprétation des résultats est basée sur l’examination desvariations simultanées des différentes charges dans le 'gap' a conduit à lier qualitativement les aspects de la photoconductivité àla structure du matériau

Numerical simulation of the steady state photoconductivity in hydrogenated amorphous silicon including localised state electron hopping

Numerical simulation of the steady state photoconductivity in hydrogenated amorphous silicon over a wide temperature range (25-500 K) is extended, to include previously neglected carrier transitions between localized states. In addition to free carrier capture (emission) transitions into (from) localized states, we include the process of electron hopping in conduction band tail states. Exponential distributions are assumed for both conduction and valence band tail states, while the dangling bond defect distribution is calculated in accordance with the defect pool model. Localized to extended state transitions follow the Simmons and Taylor statistics, and localized to localized state transitions involve electron hopping between nearest neighbour sites. Comparison with simulations in the absence of electron hopping reveals a smooth transition around 110 K, between regions of (high temperature) extended state conduction and (low temperature) hopping conduction. A hopping transport energy level is identified as the peak of the energy distribution of the hopping photocarriers, and shows a temperature dependence in agreement with existing theoretical work

Effect of Temperature on the Performance of CGS/CIGS Tandem Solar Cell

The CGS and CIGS being promising materials for large scale photovoltaic applications, the effect of temperature on the electrical parameters of a CGS/CIGS tandem solar cell has been investigated in this work. The copper gallium diselenide (CGS) and copper indium gallium diselenide (CIGS) structures as topcell and bottom-cell respectively, were numerically simulated under AM1.5G spectral illumination using the two-dimensional device simulator Silvaco-Atlas. The temperature dependency of the solar cell’s characteristics was investigated in the temperature range from 300 to 400 K at intervals of 20 K. The simulation results show the density current (Jsc) slightly increases whereas the open-circuit voltage (Voc) and fill factor (FF), conversion efficiency (ƞ) decreases with the increase in temperature. The tandem cell operating temperature efficiency was found to be (– 0.34 %/K), which is slightly higher than that of CGS solar cell (– 0.29 %/K), but markedly better than that of CIGS solar cell (– 0.41 %/K)

Irradiation-induced gold silicide formation and stoichiometry effects in ion beam-mixed layer

The irradiation-induced silicide formation in ion beam-mixed layer of Au/Si(1 0 0) system was investigated by using 200 keV Kr+ and 350 keV Xe+ ions to fluences ranging from 8×1014 to 1×1016 ions/cm2 at room temperature. The thickness of Au layer evaporated on Si substrate was ∼500 Å. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the irradiation effects on the mixed layers. We observed that at the fluence of 1×1016 Kr+/cm2 and starting from the fluence of 8×1014 Xe+/cm2, a total mixing of the deposited Au layer with Si was obtained. RBS data corresponding to the fluences of 1×1016 Kr+/cm2 and 8×1014 Xe+/cm2 clearly showed mixed layers with homogenous concentrations of Au and Si atoms which can be attributed to gold silicides. The samples irradiated to fluences of 1×1016 Kr+/cm2 and 1×1016 Xe+/cm2 were also analyzed by X-ray photoelectron spectroscopy (XPS). The observed chemical shift of Au 4f and Si 2p lines confirmed the formation of gold silicides at the surface of the mixed layers. Au2Si phase is obtained with Kr+ irradiation whereas the formed phase with Xe+ ions is more enriched in Si atoms. © 2006 Elsevier Ltd. All rights reserve

Assessment of the state of pollution by heavy metals in the surficial sediments of Algiers Bay

Sediment samples were collected at 33 stations from Algiers Bay to determine potential sources of pollution. The analyses were made with X-ray ¯uorescence (XRF). The results give information about the level of concentrations for Cr, Mn, Fe, Cu, Zn and Pb. Except for Mn and Fe which present a particular distribution (unrelated to the sedimentary facies), the distribution of the different heavy metals is irregular and depends on the bay morphology. The level of pollution by heavy metals of the bottom sediments in Algiers Bay has been shown to be significant compared with that of Surkouf, considered to be a region with low anthropogenic activity. Comparison with previous studies shows: no dependence of the assignation of Mn and Fe on sedimentary facies; high concentration of Cu, Pb and Zn in the vases and high concentration of Cr in the sands with a fine fraction between 50% and 75%