La realización de esta tesis doctoral permitió confirmar la combinación exitosa de la configuración de láseres guiados y las propiedades espectroscópicas de los dobles tungstatos de potasio y tierra rara para ser usados en la fabricación de dispositivos de óptica integrada. Mediante crecimiento epitaxial en fase líquida (LPE) de capas monocristalinas de KY1-x-yGdxLuy(WO4)2 activadas con Er3+ y Tm3+ se fabricaron guías de onda planas. Usando la composición KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 se demostró por primera vez un láser guiado en los regímenes continuo y pulsado (Q-switch) con emisión a 1.84 m. Combinando técnicas de fotolitografía UV, Ar-ion milling y LPE, se fabricaron guías de onda acanaladas de dos tipos: superficiales y soterradas. Mediante esta novedosa combinación, se demostró por primera vez un láser guiado de Tm3+ con emisión a 1.84 m sin la necesidad de añadir espejos a la guía acanalada soterrada. / The successful combination of the advantages of the waveguide laser geometry and the spectroscopic properties of monoclinic double tungstates was confirmed in this work by the realization of planar and channel waveguide lasers activated with Tm3+. Planar waveguides activated with Er3+ and Tm3+ were fabricated by Liquid Phase Epitaxial growth (LPE) of KY1-x-yGdxLuy(WO4)2 single crystalline layers over KY (WO4)2 substrates. CW and Q-switch laser operation at 1.84 m were, for the first time, demonstrated using the lattice matched composition KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 . Surface channel waveguides were fabricated by structuring the surface of the Er3+ and Tm3+-doped planar waveguides by means of standard UV-photolithography and Ar-ion milling. Buried channel waveguides were fabricated by a novel combination of LPE of the activated layers after structuring of the surface of the KY (WO4)2 substrates by Ar-ion milling. Mirrorles waveguide laser in CW regime was demonstrated using these buried channel waveguides.

No description available.

Piezoelectric materials are well known for their applications in surface (SAW) and bulk acoustic wave (BAW) devices such as oscillators, resonators and sensors. Quartz has been the main material used in such applications. Ternary calcium gallium germanate (CGG) structure-type materials, so-called langasites, recently emerged as very promising because of their piezoelectric properties superior to quartz. This thesis discusses the growth of langasite-type La3Ga5.5Ta0.5O14 (LGT) films by liquid phase epitaxy (LPE) technique and their chemical and structural characterization. In addition, the different techniques suitable for the growth of LGT are discussed and compared. To adjust the materials properties for given applications, doping by selected ions can be used. However, the dopants must be homogeneously distributed. In the current study, Al, Ti, Cr and Ca were investigated as dopants. In an earlier study, Al and Ti had been chosen because of their ability to substitute the octahedral site of LGT, normally occupied by Ga (CN=VI) with a segregation coefficient near unity in Czochralski growth. Doping with Ca and Cr has never been reported before, and therefore, the segregation behavior was unknown. In this study, Al, Ti and co-doping with Cr and Ca has been investigated for both X and Y-oriented films. The dopant distribution in the films was quantitatively evaluated by Secondary Ion Mass Spectroscopy (SIMS), using ion-implanted LGT substrates as standards. The drop of dopant concentration, in the SIMS profile, allows for the identification of the film-substrate interface and to accurately measure the thickness of the films. The film thickness is found to be typically of the order 0.5 to 2µm, depending on growth conditions. The solvent was found a reliable choice, as solvent ions were not incorporated in the films above the detection limits of the characterization techniques. A lead oxide solvent system is used as a solvent for the growth of LGT LPE films with different orientations. Extensive structural characterization was performed. The crystallinity of substrates and films grown with different orientations was compared by X-ray diffraction (XRD). The films show a very high structural perfection, with typically FWHM values of 0.035 for the (004) reflection of the XRD rocking curve. The films were also characterized by TEM. The optical transmittance of the films was characterized by Varian optical spectrophotometer, and the value obtained of approximately 80% is comparable with the transmittance value of the Czochralski grown polished substrate.

<p>Preparing silicon wafers is a tedious multi-step process that includes etching, polishing, and cleaning. The minimum wafer thickness attainable in current high volume wafer production processes is generally 160 to 300 μm, and the kerf loss for these processes is up to 40% of the total volume. Thin silicon wafers (~30 to 100μm) are very expensive to produce and the wafering process is not cost effective due to the high amount of material loss (more than 80% at these dimensions) during the process and the risk of breakage of the wafers during wafering. In this thesis, a new method called Vapour-Liquid Interface Growth (VLIG) is proposed. VLIG is capable of directly growing a sheet of single crystal silicon without wafering with a thickness of about 30 to 50μm. The features of the process are 1) low temperature operation; 2) the resulting silicon sheet is easily detachable and self-supporting; 3) the resulting sheet has uniform thickness and is single crystal. The system operates in a supersaturated growth solution of an indium-silicon melt. A seed line in a substrate facing down is employed. A layer of single crystal silicon grows on the seed line at the melt surface due to surface segregation during the super cooling process. The grown silicon can grow laterally due to the limited thickness of the melt depth that minimizes growth in the vertical growth direction. The grown silicon can be easily peeled off from the seed line substrate due to the presence of a gap between the grown silicon sheet and the oxide layer on the seed line substrate. The self-supporting silicon sheet now comprises a very thin silicon substrate or sheet.</p> <p>VLIG silicon sheet is characterized by X-ray diffraction to determine the crystallinity. Hall Effect measurements are performed to measure the electrical properties. VLIG silicon sheet is (111) oriented single crystal and it exhibits the same orientation as the substrate. The growth temperature is from 975 to 850^oC, and the VLIG silicon is p-type doped with indium. The resistivity is 4.181x10^-3 ohm-cm, and the doping level is around 5.3.0x10¹⁸ /cm3. The measured mobility is ranging from 280 cm²/V.s. In this study, VLIG demonstrates the potential of growing thin sheet of single crystal silicon with qualities that feasible for photovoltaic application.</p> / Master of Applied Science (MASc)

This thesis discusses the growth of thin-film silicon layers suitable for solar cells using liquid phase epitaxy and the behaviour of oxide LPCVD silicon nitride stacks on silicon in a high temperature ambient.¶ The work on thin film cells is focussed on the characteristics of layers grown using liquid phase epitaxy. The morphology resulting from different seeding patterns, the transfer of dislocations to the epitaxial layer and the lifetime of layers grown using oxide compared with carbonised photoresist barrier layers are discussed. The second half of this work discusses boron doping of epitaxial layers. Simultaneous layer growth and boron doping is demonstrated, and shown to produce a 35um thick layer with a back surface field approximately 3.5um thick.¶ If an oxide/nitride stack is formed in the early stages of cell processing, then characteristics of the nitride may enable increased processing flexibility and hence the realisation of novel cell structures. An oxide/nitride stack on silicon also behaves as a good anti- reflection coating. The effects of a nitride deposited using low pressure chemical vapour deposition on the underlying wafer are discussed. With a thin oxide layer between the silicon and the silicon nitride, deposition is shown not to significantly alter effective life-times.¶ Heating an oxide/nitride stack on silicon is shown to result in a large drop in effective Lifetimes. As long as at least a thin oxide is present, it is shown that a high temperature nitrogen anneal results in a reduction in surface passivation, but does not significantly affect bulk lifetime. The reduction in surface passivation is shown to be due to a loss of hydrogen from the silicon/silicon oxide interface and is characterised by an increase in Joe. Higher temperatures, thinner oxides, thinner nitrides and longer anneal times are all shown to result in high Joe values. A hydrogen loss model is introduced to explain the observations.¶ Various methods of hydrogen re-introduction and hence Joe recovery are then discussed with an emphasis on high temperature forming gas anneals. The time necessary for successful Joe recovery is shown to be primarily dependent on the nitride thickness and on the temperature of the nitrogen anneal. With a high temperature forming gas anneal, Joe recovery after nitrogen anneals at both 900 and 1000oC and with an optimised anti-reflection coating is demonstrated for chemically polished wafers.¶ Finally the effects of oxide/nitride stacks and high temperature anneals in both nitrogen and forming gas are discussed for a variety of wafers. The optimal emitter sheet resistance is shown to be independent of nitrogen anneal temperature. With textured wafers, recovery of Joe values after a high temperature nitrogen anneal is demonstrated for wafers with a thick oxide, but not for wafers with a thin oxide. This is shown to be due to a lack of surface passivation at the silicon/oxide interface.

Efficiency droop is a critical issue for the Group III-nitride based light-emitting diodes (LEDs) to be competitive in the general lighting application. Carrier spill-over have been suggested as an origin of the efficiency droop, and an InAlN electron-blocking layer (EBL) is suggested as a replacement of the conventional AlGaN EBL for improved performance of LED. Optimum growth condition of InAlN layer was developed, and high quality InAlN layer was grown by using metalorganic chemical vapor deposition (MOCVD). A LED structure employing an InAlN EBL was grown and its efficiency droop performance was compared with a LED with an AlGaN EBL. Characterization results suggested that the InAlN EBL delivers more effective electron blocking over AlGaN EBL. Hole-injection performance of the InAlN EBL was examined by growing and testing a series of LEDs with different InAlN EBL thickness. Analysis results by using extended quantum efficiency model shows that further improvement in the performance of LED requires better hole-injection performance of the InAlN EBL. Advanced EBL structures such as strain-engineered InAlN EBL and compositionally-graded InAlN EBLs for the delivery of higher hole-injection efficiency were also grown and tested.

<p>A modified liquid phase epitaxy (LPE) technique, called lateral diffusion LPE (LDLPE), is invented for low cost and high efficiency solar cell applications. Potentially, LDLPE is able to produce single crystalline silicon wafers directly from the raw material, rather than cutting wafers from single crystalline silicon ingots, therefore reducing the cost by avoiding the cutting and polishing processes.</p> <p>By using a traditional LPE method, the silicon is epitaxially grown on the silicon substrate by cooling down the saturated silicon/indium alloy solution from a high temperature. The silicon precipitates on the substrate since its solubility in the indium solvent decreases during the cooling process. A SiO₂ mask is formed on the (111) substrate with 100µm wide opening windows as seedlines. Silicon is epitaxially grown on the seedline and forms thick epitaxial lateral overgrowth (ELO) layers on the oxide mask. The ELO layers are silicon strips with an aspect ratio of 1:1 (width: thickness), approximately. The strip grows both laterally in width and vertically in thickness.</p> <p>The concept of LDLPE is to intentionally block the silicon diffusion path from the top of the seedline, but leave the lateral diffusion path from the bulk indium melt to the seedline. Theoretically, by using the LDLPE method, the silicon strip should have a larger aspect ratio, because the laterally growth in width is allowed but the vertical growth in thickness is limited. In addition, single crystalline silicon wafers can be achieved if the strip grows continuously.</p> <p>A graphite slide boat is designed to place a plate over the seedline to block the diffusion path of silicon atoms from the top of the seedline. After one growth cycle, silicon strips grown by LDLPE are wider than LPE strips but have similar thicknesses. The aspect ratios are increased from 1:1 to a number larger than 2:1. A Monte-Carlo random walk model is used to simulate the change of LDLPE strip aspect ratio caused by placing a plate over the seedline.</p> <p>Wetting seedline by indium melt is very critical for a successful growth. Due to the small space between the plate and seedline and the surface tension of the indium melt, the indium melt cannot flow into the small space. A pre-wetting technique is used to fill the space prior to loading the graphite boat into the tube furnace and solve the wetting problem successfully.</p> <p>The structure of a LDLPE silicon strip is characterized by X-ray diffraction. The electrical properties are characterized by Hall Effect measurement and photoconductive decay measurement. LDLPE silicon strips are (111) orientated single crystal and are the same orientation as the substrate. For the growth temperature of 950°C, the LDLPE strip has an estimated effective minority carrier lifetime of 30.9µs. The experimental results demonstrate that LDLPE is feasible for photovoltaic application if continuous growth and scaling up can be achieved.</p> / Doctor of Philosophy (PhD)

Une solution pour réduire la consommation de Si de haute pureté dans les cellules solaires à base de Si cristallin est de faire croître une couche active mince de haute qualité sur un substrat à faible coût. L'Epitaxie en Phase Liquide (EPL) est l'une des techniques les plus appropriées, car la croissance est réalisée dans des conditions proches de l'équilibre. On s'intéresse plus particulièrement au développement et l'optimisation d'une technique de croissance stationnaire et isotherme basée sur l'évaporation du solvant : l'Epitaxie en Phase Liquide par Evaporation d'un Solvant métallique (EPLES). Les principaux critères concernant le choix du solvant, de l'atmosphère de croissance et du creuset sont d'abord présentés et permettent de concevoir une première configuration d'étude. Un modèle analytique est ensuite développé pour comprendre les mécanismes mis en œuvre et étudier la cinétique d'évaporation du solvant et de croissance. Les différentes étapes du procédé de croissance dans le cas de l'EPLES de Si sont examinées et mettent en évidence un certain nombre de difficultés technologiques liées à cette technique : contrôle de la convection dans le bain, réactivité du bain Si-M avec le creuset, transport par différence de température et dépôt pendant la phase de refroidissement. Des solutions techniques sont proposées et mise en place pour contourner les difficultés rencontrées. Des couches épitaxiées de Si uniformes comprises entre 20 et 40 µm sont alors obtenues par EPLES avec des bains Sn-Si et In-Si sur substrat Si monocristallin entre 900 et 1200°C sous vide secondaire. Les vitesses de croissance expérimentales atteintes sont comprises entre 10 et 20 µm/h et sont conformes aux prédictions du modèle cinétique. La qualité structurale obtenue est comparable à celle des couches obtenues par EPL. Des couches de type P, avec un bain dopé In et In(Ga) sont obtenues avec une concentration en dopants proches de 1017 at.cm3 compatible avec une application PV. Enfin le potentiel de l'application de cette technique est évalué en basant la discussion sur la réalisation d'une couche de Si obtenue par EPLES sur substrat multicristallin avec un bain In-Si. / Crystalline Si thin films on low-cost substrates are expected to be alternatives to bulk Si materials for PV applications. Liquid Phase Epitaxy (LPE) is one of the most suitable techniques for the growth of high quality Si layers since LPE is performed under almost equilibrium conditions. We investigated a growth technology which allows growing Si epitaxial thin films in steady temperature conditions through the control of solvent evaporation from a metallic melt saturated with silicon: Liquid Phase Epitaxy by Solvent Evaporation (LPESE). We studied the main requirements regarding selection of solvent, crucible and growth ambient, and a first experimental set up is designed. An analytical model is described and discussed, aiming to predict solvent evaporation and Si crystallization rate. Growth experiments are implemented with a vertical dipping system. Growth procedure is presented and the influence, on Si growth, of melt convection, temperature gradient in the melt and Si-M reactivity with the material crucible are discussed. Solutions are proposed to improve and optimise the growth conditions. Experimentally, Si thin films were grown from Sn-Si and In-Si solution at temperatures between 900 and 1200°C under high vacuum. We are able to achieve epitaxial layers of several micrometers thickness (20-40µm). The predicted solvent evaporation rate and Si growth rate are in agreement with the experimental measurements. Regarding the structural quality, it is comparable to the crystal quality of layers grown by LPE. With In and In(Ga) melts, we can obtain P-type epitaxial layers with doping level in the range 1017 at.cm3, which is of great interest for the fabrication of solar cells. Finally, the growth of Si thin films on multicrystalline Si substrates by LPESE is discussed to assess the potential application of this technique.

Les détecteurs de rayon-X utilisés pour l'imagerie à haute résolution (micromètrique ou submicronique) utilisés aux synchrotrons sont pour la plupart basés sur un système de détection indirecte. Les rayons X ne sont pas directement convertis en signal électrique. Ils sont absorbés par un scintillateur qui est un matériau émettant de la lumière à la suite de l'absorption d'un rayonnement ionisant. L'image émise sous forme de lumière visible est ensuite projetée par des optiques de microscopie sur une camera 2D de type CCD ou CMOS. De nos jours, il existe différents types des scintillateurs. On distingue entre autres des scintillateurs en poudre compactée, micro structurés, céramique poly-cristalline et monocristalline. L’obtention d’une image de très bonne qualité avec une résolution spatiale au-dessous du micromètre requiert le choix d’une couche mince (1-20 µm) monocristalline. Ces types des scintillateurs peuvent être déposes sur un substrat par épitaxie en phase liquide. La très faible efficacité d’absorption dans une couche mince en fait sa faiblesse, surtout pour des énergies au-dessus de 20 keV. A l’ESRF (le synchrotron européen) des énergies jusqu'à 120 keV peuvent être exploitées pour l’imagerie. Des nouveaux scintillateurs sont donc toujours recherchés pour pouvoir améliorer le compromis entre l’efficacité d’absorption et la résolution spatiale. Dans la première partie de cet travail, un model qui décrit les détecteurs indirects pour la haute résolution, est présenté. Cet model permet de calculer la MTF (fonction de transfert de modulation) du système et peut être utilisé pour trouver la combinaison optimal de scintillateur et d’optique selon l’énergie des rayons X. Les simulations ont guidées le choix des scintillateurs à développer par épitaxie.Dans la deuxième partie, deux nouveaux types de scintillateurs développés et caractérisés dans le cadre de ce projet de thèse sont introduits : les couches minces basées sur des monocristaux de gadolinium lutétium aluminium pérovskite (GdLuAP:Eu) et d’oxyde de lutétium (Lu2O3:Eu) / X-ray detectors for high spatial resolution imaging are mainly based on indirect detection. The detector consists of a converter screen (scintillator), light microscopy optics and a CCD or CMOS camera. The screen converts part of the absorbed X-rays into visible light image, which is projected onto the camera by means of the optics. The detective quantum efficiency of the detector is strongly influenced by the properties of the converter screen (X-ray absorption, spread of energy deposition, light yield and emission wavelength). To obtain detectors with micrometer and sub-micrometer spatial resolution, thin (1-20 µm) single crystal film scintillators are required. These scintillators are grown on a substrate by liquid phase epitaxy. The critical point for these layers is their weak absorption, especially at energies exceeding 20 keV. At the European Synchrotron radiation Facility (ESRF), X-ray imaging applications can exploit energies up to 120 keV. Therefore, the development of new scintillating materials is currently investigated. The aim is to improve the contradictory compromise between absorption and spatial resolution, to increase the detection efficiency while keeping a good image contrast even at high energies.The first part of this work presents a model describing high-resolution detectors which was developed to calculate the modulation transfer function (MTF) of the system as a function of the X-ray energy. The model can be used to find the optimal combination of scintillator and visible light optics for different energy ranges, and it guided the choice of the materials to be developed as SCF scintillators. In the second part, two new kinds of scintillators for high-resolution are presented: the gadolinium-lutetium aluminum perovskite (Gd0.5Lu0.5AlO3:Eu) and the lutetium oxide (Lu2O3:Eu) SCFs

Mit der vorliegenden Arbeit wird das Wachstum von polykristallinem Silicium auf Glas bei niedrigen Temperaturen aus metallischen Lösungen in einem Zweistufenprozess untersucht. Im ersten Prozessschritt werden nanokristalline Siliziumschichten (nc-Si) hergestellt, entweder durch die direkte Abscheidung auf geheizten Substraten oder durch als ''Amorphous-Liquid-Crystalline''(ALC)-Umwandlung bezeichnete metall-induzierte Kristallisation. Im zweiten Prozessschritt dienen die Saatschichten als Vorlage für das Wachstum von deutlich größeren Kristalliten durch stationäre Lösungszüchtung. Die ALC-Prozessdauer konnte durch umfassende Parameterstudien signifikant reduziert werden. Die Charakterisierung der durch direkte Abscheidung auf geheizten Substraten entstehenden nc-Si Saatschichten offenbarte, dass es sich dabei um individuelle Saatkörner handelt, die in eine quasi-amorphe Matrix eingebettet sind. Die Oxidation der Saatschichten vor dem zweiten Prozessschritt wurde als ein wesentliches Hindernis für das Wachstum identifiziert. Als erfolgreichste Lösung zur Überwindung dieses Problems hat sich ein anfänglicher Rücklöseschritt erwiesen. Da diese Methode jedoch schwierig zu kontrollieren ist, wurde ein UV-Laser-System entwickelt und installiert. Erste Resultate zeigen epitaktisches Wachstum an den Stellen, an denen das Oxid entfernt wurde. Bei der Lösungszüchtung auf ALC-Schichten beginnt das Wachstum an einigen größeren Saatkristallen, von wo aus umliegende Gebiete lateral überwachsen werden. Obwohl Kristallitgrößen bis zu 50 Mikrometern erreicht wurden, war es noch nicht möglich, geschlossene Schichten zu erzielen. Durch Lösungszüchtung auf nc-Si Saatschichten hingegen konnte dieses Ziel erreicht werden. Geschlossene, polykristalline Si-Schichten wurden erzeugt, auf denen alle Si-Kristallite miteinander verbunden sind. Neben den Wachstumsexperimenten wurden 3D-Simulationen durchgeführt, in denen u.a. unterschiedliche Heizerkonfigurationen simuliert wurden. / The subject of this thesis is the investigation of the growth of polycrystalline silicon on glass at low temperatures from metallic solutions in a two-step growth process. In the first process step, nanocrystalline Si (nc-Si) films are formed either by direct deposition on heated substrates, or by a metal-induced crystallization process, referred to as amorphous-liquid-crystalline (ALC) transition. In the second process step, these seed layers serve as templates for the growth of significantly larger Si crystallites by means of steady-state solution growth. Extensive parameter studies for the ALC process helped to bring down the process duration significantly. Characterization of the nc-Si seed layers, formed by direct deposition on heated substrates, showed that the layer is composed of individual seeds, embedded in a quasi-amorphous matrix. The oxidation of the seed layers prior to the second process step was found to be a major obstacle. The most successful solution has been an initial melt-back step. As the process is hard to control, though, a UV laser system has been developed and installed. First promising results show unobstructed epitaxial growth where the oxide has been removed. Steady-state solution growth on ALC seed layers was found to start from a few larger seed crystals, and then cover the surrounding areas by lateral overgrowth. Although crystallites with sizes of up to 50 micrometers were obtained, it was not yet possible to achieve full surface coverage with a continuous layer. By solution growth on nc-Si seed layers, however, it was eventually possible to achieve this goal. Continuous, polycrystalline Si layers were grown, on which all Si crystallites are interlocked. The growth experiments were accompanied by 3D simulations, in which e.g. different heater configurations have been simulated.