abstract: In this project, current-voltage (I-V) and Deep Level Transient Spectroscopy (DLTS) measurements are used to (a) characterize the electrical properties of Nb/p-type Si Schottky barriers, (b) identify the concentration and physical character of the electrically active defects present in the depletion region, and (c) use thermal processing to reduce the concentration or eliminate the defects. Barrier height determinations using temperature-dependent I-V measurements indicate that the barrier height decreases from 0.50 eV to 0.48 eV for anneals above 200 C. The electrically-active defect concentration measured using DLTS (deep level transient spectroscopy) drops markedly after anneals at 250 C. A significant increase in leakage currents is almost always observed in near-ideal devices upon annealing. In contrast, non-ideal devices dominated by leakage currents annealed at 150 C to 250 C exhibit a significant decrease in such currents. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

Le nouveau procédé d’élaboration par solidification dirigée de lingots de Si quasi-monocristallin (« monolike ») offre une alternative séduisante à l’utilisation plus coûteuse de monocristaux pour la fabrication de cellules photovoltaïques à architecture avancée et haut rendement. Toutefois, la présence locale de zones de fortes densités de dislocations entraîne une dispersion des rendements obtenus.Cette Thèse présente une analyse détaillée des mécanismes de formation des structures de dislocations lors de la cristallisation monolike et de leur influence sur les propriétés électriques du matériau. Des conclusions pratiques en sont tirées pour l’amélioration du procédé.Des expériences de cristallisation en four pilote ont été réalisées en faisant varier les paramètres tenant à la mise en œuvre du pavage de germes et à la réutilisation de ceux-ci, à l’orientation cristallographique de croissance, et au dopage en élément durcissant (Ge). Des tests complémentaires de recuit et de flexion 4 points à haute température ont été utilisés pour analyser l’influence du niveau de contrainte et du temps.Une caractérisation avancée des structures de dislocations a été réalisée par imagerie X synchrotron. En arrière du front de croissance, les dislocations s’organisent en structures cellulaires qui correspondent à l’état final de fluage stationnaire. Les dislocations qui émergent au front peuvent, par accumulation locale, générer des domaines désorientés de forme conique, qui présentent des angles de rotation croissants autour de la direction de solidification, et s’étendent latéralement lors de la progression du front. Les fortes activités recombinantes de ces défauts ont été caractérisées par LBIC et Photoluminescence. Un choix approprié des orientations et des conditions de mise en œuvre des germes permet de s’affranchir des défauts initiés à l’interface germes/lingot. Toutefois, de tels défauts peuvent aussi être générés par accumulation locale de dislocations en partie supérieure des lingots sous l’effet de contraintes élevées.Ces derniers défauts n’ont pas été observés dans les lingots cristallisés dans les directions <110> et <112>, ce qui constitue un avantage par rapport aux lingots <100>. Par contre, des macles et sous-joints se sont propagés à partir des joints de grains de rotation créés volontairement, de sorte que l’effet de l’angle de rotation reste à analyser. Enfin, l’addition de germanium s’est révélée très efficace pour ralentir la multiplication des dislocations lors de tests de flexion sous faibles contraintes. Toutefois, son application à la cristallisation nécessitera une meilleure planéité du front de cristallisation et un brassage forcé du bain pour éviter une ségrégation radiale de Ge. L’utilisation d’autres éléments durcissants est également envisagée. / The new generation of directionally solidified “monolike” Si ingots presents an attractive alternative to high-cost monocrystals for the manufacture of high performance solar cells with advanced architecture. However, local zones with high densities of dislocations still affect the overall solar cell efficiency.In the present work, the mechanisms of formation of dislocations structures during monolike growth and their influence on the electrical properties of the material were analyzed, and practical conclusions were drawn for the improvement of the process.Pilot scale crystal growth experiments were performed with varying parameters related to seed pavement and seed recycling, crystallographic orientation of the growth, and doping with a strengthening element (Ge). Complementary annealing and 4-point bending tests at high temperature were used to analyze the influence of stress level and time under stress.Advanced structural characterization of dislocations structures was performed by synchrotron X-ray imaging. Behind the growth front, dislocations organize in cellular patterns which correspond to a quasi-stationary creep stage, reached in the solid after long time under stress at high temperature. Dislocations that emerge at the growth front develop, from local sources, cone-shaped misoriented domains, which present increasing tilt around the growth axis and expand laterally as growth proceeds. Characterization by LBIC and Photoluminescence showed that these defects have the highest recombination activities. The sources of these defects located at the seed ingot interface can be suppressed by proper choice of seeds orientations and arrangement. However, another source is bunching of dislocations at the growth front under the higher stresses upper in the ingot.In <110> and <112> grown ingots, dislocation bunching was not observed inside the monocrystalline parts, which shows an advantage of these orientations over <100>. On another hand, twins and sub-grain boundaries propagated from higher angle grain boundaries with these growth directions, and further studies are needed to prevent the generation of such defects. Finally, Ge doping was effective to reduce dislocations multiplication in bending under low stresses. However, its application to crystal growth will require a planar growth interface, and forced melt mixing to avoid Ge radial segregation. New researches inspired by the addition of strengthening elements are now in development.

Many smooth, highly specular coatings such as automotive paints are subjected to considerable performance demands as the customer expectations for appearance of coatings are continually increasing. Therefore it is vital to develop robust methods to monitor surface quality online. An automated visual assessment of specular coated surface that would not only provide a cost effective and reliable solution to the industries but also facilitate the implementation of a real-time feedback loop. The scope of this thesis is a subset of the inspection technology that facilitates real-time close loop control of the surface quality and concentrates on one common surface defect the seed defect. This machine vision system design utilizes surface reflectance models as a rational basis. Using a single high-contrast image the height of the seed defect is computed; the result is obtained rapidly and is reasonably accurate approximation of the actual height.

Optical three dimensional (3D) mapping routines are used in inspection robots to detect faults by creating 3D reconstructions of environments. To detect surface faults, sub millimeter depth resolution is required to determine minute differences caused by coating loss and pitting. Sensors that can detect these small depth differences cannot quickly create contextual maps of large environments. To solve the 3D mapping problem, a sensor fused approach is proposed that can gather contextual information about large environments with one depth sensor and a SLAM routine; while local surface defects can be measured with an actuated optical profilometer. The depth sensor uses a modified Kinect Fusion to create a contextual map of the environment. A custom actuated optical profilometer is created and then calibrated. The two systems are then registered to each other to place local surface scans from the profilometer into a scene context created by Kinect Fusion. The resulting system can create a contextual map of large scale features (0.4 m) with less than 10% error while the optical profilometer can create surface reconstructions with sub millimeter resolution. The combination of the two allows for the detection and quantification of surface faults with the profilometer placed in a contextual reconstruction. / Master of Science

In this project, the possibility of using thermography as a non-destructive testing tool in the manufacturing process of boats and to assess the quality of end-of-life composite structures has been explored. To do so, a literature surview regarding the current applications of thermography and the techniques currently used for quality control in the boats industry has been conducted. Additionally, the set-up of the thermal camera has been improved for the testing and measurements on several composite parts have been performed. Here, the resulting images were analysed regarding different features important for the intended new application, such as existence of delamination, bonding quality, and fibre orientations. The technique appears to be well suited to evaluate the bonding quality in case of glass fibre composite plates and to detect delaminations and other defects in such. Regarding the fibre orientation more studies are needed to judge the practicality.

No description available.

No description available.

Recombination mechanisms in gallium arsenide have been studied using temperature-dependent time-resolved photoluminescence-decay. New analytical methods are presented to improve the accuracy in bulk lifetime measurement, and these have been used to resolve the temperature-dependent lifetime. Fits to temperature-dependent lifetime yield measurement of the radiative-efficiency, revealing that samples grown by the Czochralski and molecular-beam-epitaxy methods are limited by radiative-recombination at 77K, with defect-mediated nonradiative-recombination becoming competitive at 300K and above. In samples grown with both doping types using molecular-beam-epitaxy, a common exponential increase in capture cross-section characterized by a high value of E_infinity=(258 +/- 1)meV was observed from the high-level injection lifetime over a wide temperature range (300-700K). This common signature was also observed from 500-600K in the hole-lifetime observed in n-type Czochralski GaAs where E_infinity=(261 +/- 7)meV was measured, which indicates that this signature parametrizes the exponential increase in hole-capture cross-section. The high E_infinity value rules out all candidate defects except for EL2, by comparison with hole-capture cross-section data previously measured by others using deep-level transient spectroscopy. / Thesis / Doctor of Philosophy (PhD)

<p>  We utilize thermoreflectance (TR) thermal imaging to experimentally study heat transport and reliability of micro to nano-scale devices. TR imaging provides 2D thermal maps with sub-micron spatial resolution. Fast thermal transients down to 50 ns resolution can be captured. In addition, finite element modeling is carried out to better understand the underlying physics of the experiment. We describe four main applications; 1) Development of a full-field thermoreflectance imaging setup with a variable optical (laser) heating source as a general characterization tool. We demonstrate the setup’s sensitivity to extract anisotropic<br> thermal conductivity of thin flms and evaluate its sensitivity for detecting buried (below the surface) defects in 3D integrated circuits. This method provides a low-cost noncontact alternative to destructive defect localization methods. It also doesn’t require any special sample<br> preparations. 2) Physics of localized electromigration-failures in metallic interconnects is investigated. One can distinguish two separate mechanisms responsible for electromigration depending on the current density and temperature gradient. 3) Thermal transport in silicon near sub-micron electrical heaters is studied. Quasiballistic and hydrodynamic (fluid-like) behavior is observed at room temperature for different device sizes and geometries. 4) Temperature-dependent thermoreflectance coefcient of phase-change materials is characterized. We focus on tungsten (W) doped VO₂ (W_0.02V_0.98O₂) compound, which experiences an insulator-to-metal transition (IMT) at ≈33 °C. Strong TR-signal non-linearity is observed at the IMT temperature. This non-linearity is used to localize the phase-change boundary with resolutions down to ≈0.2 µm. TR full-feld imaging enables a simple and fast characterization complementing near-feld microscopy techniques. <br>  </p>