We have observed a large spin-splitting in device made of AlxGa1-xN/GaN quantum wires. Based on this observation, we proposed a new spintronic application, the spin-hall quantum-ring interferometer, by the spin-Hall effect, Rashba and Dresselhaus effects. This device we use the ICP Etch System to etch the contact pattern, and then use the Multi-Target Sputter to deposit the protecting layer, and then use the E-Beam Evaporator to make the contact. Finally, using the Focus Ion Beam, we fabricate the quantum-ring and gate successfully. This thesis is focused on discussing the design of the fabrication and try to solve the problem in order to be able to detect the signal of the quantum-ring interferometer at low temperature and high magnetic condition.

This thesis will talk about the difference between c-plane and m-plane GaN. We use C-V measurement and try to find the difference from C-V result. We use atomic layer deposit (ALD) to deposit Al2O3 no n-Si (111), p-Si (111), c-GaN, m-GaN, c-InN and m-InN for making MOS structure. And use 100 kHz to measure high frequency C-V and charge-voltage method to measure quasi-static capacitance and leakage current. The process and how the instrument work will present in article. In Si (111) case, the flat-band voltage is far away from ideal value. This tells us charge in oxide. Result of quasi-static method shows interface state density is between 1011 cm-2¡DeV-1 to 1012 cm-2¡DeV-1. From Ref. 13, SiO2-Si system with 1011 cm-2 interface trap charge density for Si (111). We compare C-V carrier concentration with Hall carrier concentration and find some difference. We put C-V result of experiment and simulated with COX and Hall carrier concentration we measured. In GaN case, here is deep depletion in C-V result. And quasi-static result also shows deep depletion of GaN. This phenomenon means generate time of hole of n-type GaN is very long. And we use light to excite electron and hole and measure C-V for average surface density of state. The density of stay of Al2O3/m-GaN and Al2O3/c-GaN system is similar. Only appearance difference between Al2O3/m-GaN and Al2O3/c-GaN is position of flat-ban voltage. flat-ban voltage of c-GaN is more negative than m-GaN. For InN, we see ¡§the middle is lower than edge¡¨ curve. Recently, few group present complete C-V curve of InN. We can not sure whether we can use typical way to analyze this data.

The objective of this thesis is to discuss the solutions investigated by AMDG (Advanced Materials and Devices Group) to reduce the "efficiency droop" effect that occurs in III-Nitrides Light Emitting Diodes (LEDs) when driven at high injection current densities. The efficiency droop refers to a decrease of the LED light emission efficiency when increases the current density from low values ~10 A/cm2 to higher values >100A/cm2. Many scientific papers have been written about the possible reasons for this phenomenon. Therefore, this thesis will discuss the different effects suspected to contribute to the droop, and discuss LED structure modifications studied by Dr. Dupuis' research group to reduce their impact. In addition to a description of a conventional LED structure, a discussion of the device fabrication process will be provided including the solutions investigated in our group to improve LED performance. Because measurement is critical to our studies, a description of the equipment used by the AMDG will be provided, e.g., the Electroluminescence (EL) and Photoluminescence (PL) test stations, Atomic Force Microscopy (AFM) for surface topology, TLM for metallic contact resistivity, X-Ray diffraction for crystal quality and epitaxial layer structure, and Hall-Effect measurement for doping concentration characterization and material resistivity. Because the IQE gives us a direct assessment of the active region's crystal quality, the setup and operation of a new Temperature-Dependent PL (TD-PL) system to measure the Internal Quantum Efficiency (IQE) was the main focus of this research. The External Quantum Efficiency (EQE) is measured using electroluminescence measurements. The EL measurements involve the acquisition of the emitted light spectrum along with different processed data such as the Full-Width at Half Maximum (FWHM) of the spectral intensity, the peak wavelength, output power, etc., which allows a comparison of the different LED structure performances. Within this work, a new LabVIEW© program (called QuickTest 2.0) has been developed in order to automate the instrumentation setup and improve both the speed and accuracy of EL acquisition. A brief description of the G language used by the LabVIEW© software will be provided along with the objective and motivation for upgrading the program, the general features of the program, and a comparison of spectrum acquisition and processed data results. The benefit for the research in the AMDG was to reduce measurement time, improve efficiency, supply a more user-friendly front-panel, and to enable transfer to other computers.

Cobham Electronic Systems, Inc. has developed a field-programmable telemetry transmitter module for higher-power (0.1W to 25W) airborne telemetry applications. A key feature of the transmitter is high DC to RF conversion efficiency over the entire variable output power range of 25dB through the use of GaN amplifiers. This high efficiency is realized by using a variable voltage DC-DC converter and dynamic bias control of the GaN amplifier elements. This feature is useful in that output power can be tailored to mission requirements and timelines, thereby extending battery life and increasing operation time. The transmitter receives configuration commands and can be programmed through an external data port. The transmitter can be configured for RF power and frequency over the telemetry S-Band frequency range, and has multiple data rates. The unit consists of RF, digital and power supply circuits. The RF transmitter is a PCM-FM type with a phase-locked loop, driver amplifiers, a power amplifier and a digital processor for RF control. The unit contains a digital processor, FPGA's, and flash memory. The power supplies contains all the regulator circuits to supply power to the rest of the unit, variable output drain voltage to the GaN devices, EMI filtering, under/overvoltage protection, a temperature sensor and a digital processor for power control. The electronics are housed in a compact aluminum housing.

This dissertation investigates the growth of high quality GaN and InN thin films by plasma assisted molecular beam epitaxy (PAMBE). It also explores the growth of self-seeded GaN branching nanowires and p-type doping of InN, two topics of particular interest at present. The growth of high quality III-Nitride semiconductor thin films have been shown to be dependent on the group-III (metal) to nitrogen ratio. A metal-rich growth environment enhances the diffusion of the group-III adatoms through the formation of a group-III adlayer. By using a metal-rich growth environment, determined by growth rate studies using laser reflection interferometry or RHEED analysis of the surface, both GaN and InN films have been grown with a smooth surface morphology. Additionally the smooth surface morphology has beneficial effects on the electrical and optical properties of both materials. However, with the growth using a metal-rich environment, group-III droplets are present on all film surfaces, which can be an issue for device fabrication, as they produce facets in the crystal structure due to enhanced growth rates. MBE growth of GaN nanowires via the vapour liquid solid (VLS) and vapour solid (VS) growth techniques have so far been based on the N-rich growth regime. However, we have shown that the Ga-rich growth regime can be used to grow self-seeded one dimensional and hierarchical GaN nanowires. 7 µm long hierarchical GaN nanowires with at least three branches were grown and shown to have a high crystalline quality. The suggested growth mechanism is a self-seeding VLS process driven by liquid phase epitaxy at the nanoscale, while the branching growth was nucleated due to the Ga-rich growth regime by excess Ga droplets forming on the trunk during growth. The growth of vertical GaN nanowires has also been achieved using the same self-seeding process and the critical parameter seems to be the Ga to N ratio. Also, the growth rate of the Ga-rich grown GaN nanowires can supersede the growth rates reported from N-rich grown GaN nanowires by at least a factor of two. The fabrication of vertical and planar GaN nanowire devices has been demonstrated in this study. Two point and three point contacts were fabricated to the branching GaN nanowires in the planar direction with resistive measurements ranging from 200 - 900 kΩ, similar to chemical vapour deposition and MBE grown GaN nanowires. The nonlinear current-voltage characteristics from the three point contacts may lead to unique nano-devices. The planar nanowires have also shown to have potential as UV detectors. Schottky diodes were fabricated on the vertical nanowires, with values for the barrier heights consistent with bulk diodes. Mg and Zn doping studies of InN were also performed. Both InN:Mg and InN:Zn have strong photoluminescence only at low doping concentrations. However, the InN:Mg films have reduced mobilities with increased Mg content, whereas the mobility determined from the InN:Zn films is independent of Zn. When the InN:Zn film quality was improved by growing under the In-rich growth regime, electrochemical capacitance-voltage results suggest n{type conductivity, and strong photoluminescence was obtained from all of the films with four features seen at 0.719 eV, 0.668 eV, 0.602 eV and 0.547 eV. The features at 0.719 eV and 0.668 eV are possibly due to a near band edge to valence band or shallow acceptor transition, while the 0.547 eV has an activation energy of 60 meV suggesting a deep level acceptor.

Ces dernières années ont vu l'avènement de diodes électro-luminescentes bleues et blanches efficaces à base de nitrure de gallium (GaN). Cette technologie est en position de remplacer les ampoules conventionnelles dans un proche futur, permettant ainsi de considérables économies d'énergie. Toutefois, ce scénario exige que ces diodes soient entièrement optimisées, depuis la qualité du matériau jusqu'à la façon d'en extraire la lumière. Cette thèse étudie ce dernier aspect : la lumière émise dans un semiconducteur y est naturellement piégée, et une stratégie est nécessaire pour briser ce mécanisme de guidage. Plus précisément, nous examinons des méthodes permettant l'extraction déterministe de la lumière des diodes GaN en utilisant ses propriétés ondu! latoire (interférences, diffraction) afin d'obtenir des diodes efficaces dont les propriétés d'émission sont contrôlées. Les diodes a microcavités sont tout d'abord envisagées : celles-ci utilisent les interférences de la lumière dans la diode pour modifier les directions préférentielles d'émission et maximiser l'extraction directe. Toutefois, la fabrication de ces structures est complexe et n'offre qu'une efficacité théorique imparfaite. Par la suite, l'extraction de la lumière guidée par cristaux photoniques (CP) est étudiée. Un CP est une structure optique périodique formée dans la diode, qui altère les propriétés de propagation de la lumière. Ici, le CP agit comme un réseau de diffraction bidimensionnel qui redirige la lumière guidée vers l'extérieur. Ce principe est tout d'abord exploré par des expériences de photoluminescence sur des structures simples, qui révèlent la structure des modes guidés et suggèrent les propriétés que le CP devrait posséder. Ces propriétés peuvent être regroupées en deux catégories : structure planaire (choix du réseau cristallin et de la période du CP...) et structure verticale (qui mêle de façon plus complexe les propriétés du CP lui-même et celles de la couche épitaxiée). Diverses implémentations de diodes à cristaux photoniques sont par la suite proposées, fabriquées et caractérisées. Divers réseaux cristallins sont comparés, révélant les avantages de motifs complexes tels que le pavage d'Archimède. La plus grande partie de l'optimisation porte cependant sur la structure verticale, afin s'assurer une extraction efficace par le CP. Plusieurs solutions sont étudiées (ingénierie des couches épitaxiales pour modifier le diagramme d'émission de la lumière, structures minces pour augmenter son interaction avec le CP...) L'ensemble de ces implémentations est validé et guidé par la modélisation des propriétés du CP. Cette modélisation est un problème numérique complexe (solution des équations de Maxwell en trois dimensions). Plusieurs codes ont été écrits et employés durant la thèse - dont une méthode originale dite " hybride ". Celle-ci a permis d'expliquer quantitativement les résultats expérimentaux, et de suggérer les voies d'optimisation étudiées par la suite. Bien que loin d'être entièrement optimisées, les diodes obtenues à l'issue de ce travail présentent des résultats encourageants et laissent espérer une application industrielle.

Understanding the magnitude of the temperature in AlGaN/GaN heterostructure fi eld e ffect transistors(HFETs) is a critical aspect of understanding their reliability and providing proper thermal management. At present, most models used to determine the temperature rise in these devices are based on continuum based heat conduction. However, in such devices, the heat generation region can be on the order of or smaller than the phonon mean free path of the heat carriers, and thus, such models may under predict the temperature. The aim of this work is towards building a multiscale thermal model that will allow for the prediction of heat transport from ballistic-diffusive phonon transport near the heat generation region and diffusive transport outside of this zone. First, a study was performed to determine the appropriate numerical solution to the phonon Boltzmann transport equation followed by its integration into a multiscale thermal scheme. The model, which utilizes a Discrete Ordinates Solver, was developed for both gray and non-gray phonon transport. The scheme was applied to the solution of speci fic test problems and then finally to the electrothermal modeling of AlGaN/GaN HFETs under various electrical bias conditions.

In Middle English and Scots, instances of gan and can behave differently from etymologically related beginnen in that they are mainly, or exclusively, found with the plain infinitive and with a non-ingressive meaning. They also occur in narrative verse (rhymed and non-alliterative), where they have a metrical, intensive-descriptive or textual function. All of this suggests that gan and can are more advanced in the divergence of their development towards auxiliation than the verb beginnen. Earlier studies mainly concentrate on the meaning and/or function of gan and can in verse (Wuth 1915, Beschorner 1920, Funke 1922, Mustanoja 1960, Kerkhof 1966, Visser 1969 and Brinton 1981; 1983; 1988 amongst others), whereas investigations by Brinton (1981; 1988; 1996), Ogura (1997; 1998; 2013) and Sims (2008; 2014) address the divergence in the development of this verb and its variant in terms of grammaticalization, but with references to Middle English in general. Studies by Los (2000; 2005), on the other hand, deal with the grammaticalization of onginnan and beginnan with the plain infinitive in Ælfric’s works. However, no studies have been carried out on whether gan and can, as well as beginnen develop differently in terms of grammaticalization in the ‘English’ of the six northern counties of England and of Scotland in the late 14th and the 15th centuries, conventionally referred to as Northern Middle English and Early Scots, respectively. With the aid of Northern Middle English and Early Scots texts from computerised corpora (The Helsinki Corpus of English Texts, The Innsbruck Corpus of Middle English Prose and The Teaching Association for Medieval Studies, as well as The Helsinki Corpus of Older Scots and A Linguistic Atlas of Older Scots), this study looks into whether: a) gan and can, as well as beginnen differ with respect to their morphological paradigms, in view of what we know about grammaticalization and the development of invariant forms? b) these verbs differ with respect to their complements, in view of claims in the literature that the more grammaticalized variant takes the plain infinitive; and c) gan and can are a development from onginnan and aginnan, originally expressing ingression but shown in the literature to have undergone semantic bleaching in Old English and in early Middle English period? This study shows that in Northern Middle English and Early Scots, gan and can display characteristics of grammaticalization, while beginnen participates in global language changes affecting the category of the verb in ME and Scots.

Gallium Nitride (GaN) is considered a very promising material for use in the field of power devices as its application in power systems would result in a significant increase in the power density, reduced power losses, and the potential to operate at high frequencies. The wide bandgap of the material allows a high critical electric field to be sustained which can lead to the design of devices with a shorter drift region, and therefore with lower on-state resistance, if compared to a silicon-based device with the same breakdown voltage. The use of an AlGaN/GaN heterostructure allows the formation of a two-dimensional electron gas (2DEG) at the heterointerface where carriers can reach very high mobility values. These properties can lead to the production of High Electron Mobility Transistors (HEMTs) and Schottky barrier diodes with superior performance, even when compared to devices based on state-of-the-art technologies such as Silicon Carbide or superjunctions. Furthermore, epitaxial growth of GaN layers on silicon wafers allows a significant reduction in the production cost and makes these devices competitive from a price perspective. This thesis will deal with a variety of topics concerning the characterization, design and optimization of AlGaN/GaN HEMTs and Schottky diodes with a 600 to 650V rating. Discussion will span several topics from device cross-section physics to circuit implementation and will be based on both experimental results and advanced modelling. More specifically, the thesis is concerned with the characterization of AlGaN/GaN Schottky diodes and extraction of their main parameters such as ideality factor, barrier height and series resistance. A thorough investigation of their reverse recovery performance and a comparison to competing technologies is also given. Several topics which concern the operation of AlGaN/GaN HEMTs are then discussed. The underlying physics of p-gate enhancement mode transistors are analysed followed by a discussion of the challenges associated with the implementation of these devices at a circuit level. Finally, a comparison of the performance of a specific area-saving layout (Bonding pad over active area) and a conventional design is given. The thesis aims to significantly enhance the understanding of the behaviour of these devices to enable better or new commercial designs to emerge.

abstract: As residential photovoltaic (PV) systems become more and more common and widespread, their system architectures are being developed to maximize power extraction while keeping the cost of associated electronics to a minimum. An architecture that has become popular in recent years is the "DC optimizer" architecture, wherein one DC-DC converter is connected to the output of each PV module. The DC optimizer architecture has the advantage of performing maximum power-point tracking (MPPT) at the module level, without the high cost of using an inverter on each module (the "microinverter" architecture). This work details the design of a proposed DC optimizer. The design incorporates a series-input parallel-output topology to implement MPPT at the sub-module level. This topology has some advantages over the more common series-output DC optimizer, including relaxed requirements for the system's inverter. An autonomous control scheme is proposed for the series-connected converters, so that no external control signals are needed for the system to operate, other than sunlight. The DC optimizer in this work is designed with an emphasis on efficiency, and to that end it uses GaN FETs and an active clamp technique to reduce switching and conduction losses. As with any parallel-output converter, phase interleaving is essential to minimize output RMS current losses. This work proposes a novel phase-locked loop (PLL) technique to achieve interleaving among the series-input converters. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014