Ces travaux de thèse ont développé l’ensemble des problématiques de diffusion liées à la fabrication de la technologie HgCdTe p/n, avec pour objectif l’obtention d’un modèle numérique permettant la simulation complète de la diode. Nous avons étudié le phénomène d’interdiffusion Hg/Cd, indispensable au processus de passivation du photodétecteur. Dans un milieu monocristallin le coefficient d’interdiffusion est calculé par la loi de Darken qui fait intervenir le facteur thermodynamique, dont nous avons déterminé la variation en température. L’exodiffusion de l’indium, le dopant n, et sa diffusion dans le HgCdTe ont aussi été étudiées. L’arsenic est utilisé comme dopant p et est donc activé en conditions riche-Hg. Nous avons tout d’abord étudié sa diffusion, tout d’abord dans des conditions classiques, puis après son incorporation dans le HgCdTe en présence de défauts hors-équilibre. / This thesis work focuses on the modeling of the different diffusion phenomena that occur during the processing steps of the p/n HgCdTe technology. Hg/Cd interdiffusion is essential for the passivation of the HgCdTe and so was addressed. In a monocrystalline material, the interdiffusion coefficient is calculated with the Darken law. It includes the thermodynamic factor which temperature dependence was determined. Indium exodiffusion and diffusion in HgCdTe were also studied. Arsenic is used as a p dopant and so is activated in Hg-rich conditions. Its diffusion was studied firstly in classic conditions, and then after its incorporation in HgCdTe with the influence of out of equilibrium point defects.

L'intégration de composants discrets sur un système unique, tel une puce électronique, augmente les performances totales du système, fait apparaitre de nouvelles fonctionnalités et diminue les coûts associés à la fabrication des dispositifs. Ces améliorations, appliquées au secteur de la microélectronique, sont grandement responsables des avancements importants qu'ont connus les technologies de l'information et des communications au cours des dernières années. Puisque la fabrication de circuits photoniques intégrés nécessite l'intégration de structures ayant des bandes interdites différentes à partir d'une même puce semiconductrice, leur niveau d'intégration est bien inférieur que celui atteint pour un microprocesseur standard. Parmi les techniques ayant le potentiel de fabriquer des circuits photoniques intégrés monolithiquement, l'interdiffusion de puits quantique post-expitaxial contrôlée spatialement augmente la bande interdite d'une hétérostructure semiconductrice à l'intérieur de régions définies. Le processus d'interdiffusion, activé thermiquement, est accéléré par la diffusion d'impuretés et de défauts ponctuels tels que les lacunes et les interstitiels. L'hypothèse de départ de mes travaux de doctorat suppose que la radiation laser ultra-violette module la diffusion et la génération de défauts ponctuels dans les hétérostructures reposant sur les technologies à base de GaAs et d'InP et, conséquemment, contrôle spatialement l'interdiffusion de puits quantiques. Nous avons démontré que lorsque appliquée sur des hétérostructures à base de GaAs, l'irradiation laser excimère l'interdiffusion en favorisant la croissance d'un stresseur de surface qui empêche la diffusion des défauts ponctuels vers les puits quantiques. Nous avons souligné l'influence de la vapeur d'eau physisorbée sur la croissance du stresseur et avons déterminé la résolution spatiale de la technique. Dans les hétérostructures basées sur les technologies InP, même sous le seuil d'ablation, l'absorption des impulsions laser UV favorise la désorption des atomes de surface ce qui génère des défauts ponctuels en concentration excédentaire. Lors d'un recuit thermique, ces défauts ponctuels augmentent la vitesse de l'interdiffusion sous les régions irradiées.

The pseudo-binary system of BaTiO3-SrTiO3 ceramics offering potential applications in the electronic industry, particularly for the passive components, has been studied for its diffuse phase transition over the temperature range of +150oC and -50oC. This research concentrating on the interdiffusion between two sintered layers of such perovskite is a continuation of study, conducted by this author¡¦s group over the past years. Two-layer BaTiO3-SrTiO3 stacks were sintered at 1300oC and annealed for various time periods to investigate if and how the interdiffusion occurs across the BaTiO3-SrTiO3 interface. Optical microscopy reveals an interface layer consisting of polytitanate second phases, which appear to be large, chunky grains initially. Both results obtained from X-ray diffractometry and micro-chemical analysis using the energy-dispersive spectrometry, equipped with the scanning electron microscopy, suggest that the second phases are: Ba4Ti13O30, Ba2Ti9O20, Ba6Ti17O40 and BaTi2O5. These polytitanates are produced from the solid-state reaction between BaTiO3 and TiO2, which is left behind in the BaTiO3 layer when Ba2+ being the faster diffusion A-site cation have moved across into the SrTiO3 layer in a significantly higher content. The interface phases grow progressively to a coherent second-phase layer upon prolonged annealing for 100 h. It is revealed by the transmission electron microscopy that residual pores, similar to the Kirkendall type in the classical Cu-Zn diffusion couple, generated at ~100 £gm away from the interface and located in the BaTiO3 layer. This is attributed to the significantly different lattice diffusivities between two A-cations, i.e. Ba2+ being faster than Sr2+ by approximately three times, with A-site vacancies ( ) created in the grains of the BaTiO3 layer. Together with B-site cation vacancy ( ) and oxygen vacancy ( ), similar to the prismatic loops formed in quenched aluminium, condensation of vacancies via a reverse Schottky defect reaction has formed such Kirkendall-like pores within BaTiO3 grains. Interdiffusion has resulted in forming the solid solutions of (Ba,Sr)TiO3, with Sr2+ being solute cation, and (Sr,Ba)TiO3, with Ba2+ being solute cation, in the initial layers, respectively, and the characteristic core-shell grains responsible for the diffuse-phase transition. A mechanism of how cation diffusion produces the core-shell grains in both layers, modified from Bow (1990) and Liu (1991), is proposed.

<p>This dissertation focuses on the development and calibration of reaction models for multilayered nanocomposites. The nanocomposites comprise sputter deposited alternating layers of distinct metallic elements. Specifically, we focus on the equimolar Ni-Al and Zr-Al multilayered systems. Computational models are developed to capture the transient reaction phenomena as well as understand the dependence of reaction properties on the microstructure, composition and geometry of the multilayers. Together with the available experimental data, simulations are used to calibrate the models and enhance the accuracy of their predictions.</p><p>Recent modeling efforts for the Ni-Al system have investigated the nature of self-propagating reactions in the multilayers. Model fidelity was enhanced by incorporating melting effects due to aluminum [Besnoin et al. (2002)]. Salloum and Knio formulated a reduced model to mitigate computational costs associated with multi-dimensional reaction simulations [Salloum and Knio (2010a)]. However, exist- ing formulations relied on a single Arrhenius correlation for diffusivity, estimated for the self-propagating reactions, and cannot be used to quantify mixing rates at lower temperatures within reasonable accuracy [Fritz (2011)]. We thus develop a thermal model for a multilayer stack comprising a reactive Ni-Al bilayer (nanocalorimeter) and exploit temperature evolution measurements to calibrate the diffusion parameters associated with solid state mixing (720 K - 860 K) in the bilayer.</p><p> </p><p>The equimolar Zr-Al multilayered system when reacted aerobically is shown to </p><p>exhibit slow aerobic oxidation of zirconium (in the intermetallic), sustained for about 2-10 seconds after completion of the formation reaction. In a collaborative effort, we aim to exploit the sustained heat release for bio-agent defeat application. A simplified computational model is developed to capture the extended reaction regime characterized by oxidation of Zr-Al multilayers. Simulations provide insight into the growth phenomenon for the zirconia layer during the oxidation process. It is observed that the growth of zirconia is predominantly governed by surface-reaction. However, once the layer thickens, the growth is controlled by the diffusion of oxygen in zirconia.</p><p>A computational model is developed for formation reactions in Zr-Al multilayers. We estimate Arrhenius diffusivity correlations for a low temperature mixing regime characterized by homogeneous ignition in the multilayers, and a high temperature mixing regime characterized by self-propagating reactions in the multilayers. Experimental measurements for temperature and reaction velocity are used for this purpose. Diffusivity estimates for the two regimes are first inferred using regression analysis and full posterior distributions are then estimated for the diffusion parameters using Bayesian statistical approaches. A tight bound on posteriors is observed in the ignition regime whereas estimates for the self-propagating regime exhibit large levels of uncertainty. We further discuss a framework for optimal design of experiments to assess and optimize the utility of a set of experimental measurements for application to reaction models.</p> / Dissertation

Thesis (doctoral)--Techn. Hochsch., Aachen, 2005.

No description available.

A new method to extract composition dependent ternary interdiffusion coefficients from a single diffusion couple experiment is presented. The calculations involve direct determination of interdiffusion fluxes from experimental concentration profiles and local integration and differentiation of Onsager's formalism. This new technique was applied to concentration profiles obtained from selected semi-infinite, single-phase diffusion couple experiments in the Cu-Ni-Zn, Fe-Ni-Al, and Ni-Cr-Al systems. These couples exhibit features such as uphill diffusion and zero flux planes. The interdiffusion coefficients from the new technique along with coefficients reported from other methods are graphed as functions of composition. The coefficients calculated from the new technique are consistent with those determined from Boltzmann-Matano analysis and an alternate analysis based on the concept of average ternary interdiffusion coefficients. The concentration profiles generated from the error function solutions using the calculated interdiffusion coefficients are in good agreement with the experimental profiles including those exhibiting uphill diffusion. The new technique is checked for accuracy and consistency by back-calculating known interdiffusion coefficients; in this exercise, the new method accurately predicts constant diffusivity. After rigorous verification, the new technique is applied to previously unexamined couples in the Ni-Pt-Al system. With Ni as the dependent component, the main coefficients are shown to be relatively constant and the cross coefficients are negative. The interdiffusion coefficient representing the contribution of the concentration gradient of Pt to the interdiffusion flux of Al is relatively large for couples whose Al content is low, indicating that Pt has a significant effect on Al when Al concentration is low. Another important aspect of analyzing diffusional interactions is the movement of single and multi-phase boundaries within a diffusion couple. Phase boundaries for an n-component system are newly classified and boundary movement is analyzed in terms of degrees of freedom. Experimental evidence of a category 2:1 boundary is presented with a solid-to-solid semi-infinite diffusion couple in the Fe-Ni-Al system with two single-phase terminal alloys. The diffusion path for this couple surprisingly passes through the vertex of the equilibrium tie triangle on the phase diagram to exhibit three phase equilibria in a ternary system. Here is shown for the first time experimental verification of this phenomenon.

No description available.

Recently Silicon Germanium alloy (Si_1-xGe_x) is showing lots of potentials in device fabrication. Most of the structures containing Si_1-xGe_x that are fabricated at present involve Si/Si_1-xGe_x heterostructure. The fabrication process involves several high temperature anneal steps in either inert, oxidizing or nitriding ambient which results the interdiffusion of Si and Ge through the hetero-interfaces. The interdiffusion causes broadening of Si/Si1_xGex interface and changes the physical position of the heterointerface which can cause degradation of device performance. Several studies have so far been done to quantify the amount of Ge interdiffusion in heterostructures. However no study has yet been performed to model this phenomenon. Modeling the interdiffusion mechanism is important for two reasons: (1) it will facilitate to calibrate the device characteristics taking the effect of interdiffusion mechanism into calculations prior to device fabrication; and (2) to get a better insight of the actual mechanism involved in the interdiffusion process. In this study, attempt has been taken to model interdiffusion of Si and Ge in structures having Si/Si_1-xGe_x hetero-interfaces. Mathematical models are proposed to model the behavior and the models are applied to previously published results where samples were annealing in inert, oxidizing and nitriding ambient at different anneal temperatures for different anneal times. First only the contributions of vacancies in the interdiffusion mechanism are considered. This can successfully model the interdiffusion mechanism for samples annealed in inert and oxidizing ambients at low temperatures (below 1050°C). Next the contributions of interstitials along with vacancy in the interdiffusion mechanism are considered. These are able to successfully model the interdiffusion phenomenon for the samples annealed in oxidizing and nitriding ambients at high temperatures (above 1050°C). The success of the modeling is justified by getting good match between the simulated and the experimental interdiffusion profiles along with good match between the fitting parameters used in the simulations compared with previous reported values. Besides modeling the interdiffusion mechanism, for the first time, a mathematical model is proposed for vacancy injection while nitridation of silicon is done. / Thesis / Master of Applied Science (MASc)

In this thesis, the interface between the electron donor polymer and the electron acceptor fullerene in organic photovoltaic devices is studied. Starting from a bilayer system of donor and acceptor materials, the proximity of polymer and fullerene throughout the bulk of the devices is improved by inducing an interdiffusion of the two materials by heating the devices in the vicinity of the glass transition temperature of the polymer. In this manner, a concentration gradient of polymer and fullerene throughout the bulk is created. The proximity of a fullerene within 10 nm of any photoexcitation in the polymer ensures that the efficient charge separation occurs. Measurements of the absorption, photoluminescence, and photocurrent spectra as well as I-V characteristics are used to study the interdiffusion and its influence on the efficiency of the photovoltaic devices. In addition, the film morphology is studied on a microscopic level with transmission electron microscopy and with Auger spectroscopy combined with ion beam milling to create a depth profile of the polymer concentration in the film. Initial studies to induce an interdiffusion were done on poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) as the electron donor polymer and the buckminsterfullerene C60 as the electron acceptor. Interdiffused devices show an order of magnitude photoluminescence quenching with concomitant increase in the photocurrents by an order of magnitude. Variation of the polymer layer thickness shows that the photocurrents increase with decreasing thickness down to 70 nm due to charge transport limitation. The choice of layer thickness in organic photovoltaic devices is critical for optimization of the efficiency. The interdiffusion process is also monitored in situ and a permanent increase in photocurrents is observed during the heat treatment. Transmission electron microscopy (TEM) studies on cross sections of the film reveal that C60 interdiffuses into the MEH-PPV bulk in the form of >10 nm clusters. This clustering of C60 is a result of its tendency to crystallize and the low miscibility of C60 in MEH-PPV, leading to strong phase separation. To improve the interdiffusion process, the donor polymer is replaced by poly(3-octylthiophene-2,5-diyl) (P3OT), which has a better miscibility with C60. Again, the photocurrents of the interdiffused devices are improved significantly. A monochromatic power conversion efficiency of 1.5 % is obtained for illumination of 3.8 mW/cm2 at 470 nm. The polymer concentration in unheated and interdiffused films is studied with Auger spectroscopy in combination with ion beam milling. The concentration profile shows a distinct interface between P3OT and C60 in unheated films and a slow rise of the P3OT concentration throughout a large cross-section of the interdiffused film. TEM studies on P3OT/C60 films show that C60 still has some tendency to form clusters. The results of this thesis demonstrate that thermally-controlled interdiffusion is a viable approach for fabrication of efficient photovoltaic devices through nanoscale control of composition and morphology. These results are also used to draw conclusions about the influence of film morphology on the photovoltaic device efficiency and to identify important issues related to materials choice for the interdiffusion process. Prospective variations in materials choice are suggested to achieve better film morphologies. / Ph. D.