Wide Bandgap Based Devices

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

Advanced GaN HEMTs for high performance microwave power amplifiers

The ever increasing demand for high power levels at higher frequencies from the industry has stimulated extensive research in gallium nitride (GaN) transistor technology over the past two decades. This has led to significant advances of the technology, but the degradation in the device performance due to device self-heating and trap generation in the device epilayers during device operation is still a major challenge with the current GaN high electron mobility transistor (HEMT) technology. This thesis focuses on minimising device self-heating effects by means of efficient heat distribution within the device. Two approaches are analysed in this work. Firstly, the impact on the device DC performance of improved wafer growth conditions by using method called hot-wall MOCVD (metal organic chemical vapour deposition) are investigated. It was found that 2 µm × 100 µm devices on this wafer exhibit only 4% degradation in the saturated output current density at 20 V compared with 13% for devices fabricated on a wafer grown by standard MOCVD growth. This improved performance was attributed to lower thermal boundary resistance achieved by improved growth quality of the epitaxial material layers. In the second approach, the impact on self-heating was investigated through the use of a distributed device channel, i.e. introducing inactive regions along the device channel to distribute the hot spots in the device. Here a planar isolation method was used to achieve planar distributed gate devices that led to low leakage currents below 200 nA/mm at gate voltage of -20 V. A decrease in the peak channel temperature of 30°C was found through thermal simulations over a single 100 µm wide gate finger. Moreover, these distributed channel devices with gate periphery of 10 ×100 µm showed 13 % higher saturated current density than standard devices with the same active device area. The other major issue addressed in this thesis is the so-called current collapse which is a degradation in the output current caused by electron trapping in the device structure. An alternative solution to the conventionally used dielectric passivation is proposed and it entails the use of a thick undoped GaN cap layer to reduce the surface effects by moving the surface further away from the device channel. Drain lag measurements show 15% and 35% decrease in the current at quiescent bias decrease points of [-7 V; 10 V] and [-7 V; 20 V] respectively for the proposed structure compared with 80% decrease and complete current collapse at these quiescent bias points in the same geometry devices on a standard wafer with 2 nm GaN cap layer and a thin 10 nm thin SiNx passivation, respectively. The 10 nm thin passivation layer does not minimise the surface effects, but it protects the devices from oxidation. Finally, a single stage class A amplifier was demonstrated using the developed technology exhibiting peak output power of 30 dBm at 10 GHz and associated power added efficiency of 44% and gain of 10 dB. Also, gain of at least 9.4 dB was shown over 8-13 GHz bandwidth

CHARACTERIZATION AND MODELING OF III-V TRANSISTORS FOR MICROWAVE CIRCUIT DESIGN

New mobile communication technologies have given a boost to innova-tions in electronic for telecommunications and microwave electronics. It’s clear that the increasing request for mobile data availability, as proved by the growth of 69% of mobile data traffic in 2014, poses great challenges to indus-tries and researchers in this field. From this point of view a rapid diffusion of wireless mobile broadband network data standards, like LTE/4G, should be seen, which requests a state-of-the-art transceiver (i.e., transmitter/receiver) electronics. It will be mandato-ry to use higher frequencies, with wider bandwidth and excellent efficiency, to improve battery duration of mobile phones and reduce the energy consump-tion of the network infrastructures (i.e. base stations). Moreover, the microwave electronics is ubiquitous in satellite systems. As an example the GPS-GLONASS systems, developed respectively by United-States and Russian Federation for geo-spatial positioning, now are commonly used as navigation support for planes, ships, trains, automobiles, and even people. Other interesting applications are the earth-observation satellites, like the Italian system COSMO-SkyMed: a constellation of four satellites developed for the observation of the entire planet. These systems are able to produce a detailed image of the earth surface exploiting a microwave synthetic aperture radar, with the possibility to observe an area even by night or with bad weather conditions. Clearly these features are impossible for traditional opti-cal systems. Even if a lot of electronic applications are focused on the system architec-ture, in microwave electronics the single transistor still plays a key role. In-deed, the number of transistors in high-frequency circuits is low and wide ar-eas are occupied by numerous passive elements, required to optimize the sys-tem performance. There is a lot of interest in finding the optimum transistor operating condition for the application of interest, because the high-frequency electron-device technologies are relatively young and often still in develop-ment, so the transistor performance is generally poor. As a matter of fact, transistor characterization plays a very important role: various measurement systems, developed for this purpose, have been pro-posed in literature, with different approaches and application fields. Moreover, a meticulous characterization of the transistor is the basis for the identification of accurate models. These models, allowing to predict the tran-sistor response under very different operating conditions, represent a funda-mental tool for microwave circuit designers. This thesis will resume three years of research in microwave electronics, where I have collaborated in research activities on transistor characterization and modelling oriented to microwave amplifier design. As various kinds of amplifiers (i.e., low-noise amplifier, power amplifier) have been developed, various characterization techniques have been exploited. In the first chapter, after a presentation of the most common large-signal characterization systems, a low-frequency large-signal characterization setup, oriented to transistor low-frequency dispersion analysis and power amplifier design, will be described as well as the development of the control algorithm of the measurement system and its application to the design of a Gallium-Nitride class-F power-amplifier, operating at 2.4 GHz with 5.5 W of output power and 81% efficiency. Another application of the proposed setup for fast-trap characterization in III-V devices is then reported. Successively, an exten-sion of the setup to very low frequencies will be presented. In the second chapter, small-signal characterization techniques will be dealt with, focusing on noise measurement systems and their applications. Af-ter a brief introduction on the most relevant small-signal measurement system (i.e., the vector network analyzer), an innovative formulation will be intro-duced which is useful to analyze the small-signal response of Gallium-Arsenide and Gallium-Nitride transistors at very low frequencies. Successive-ly, the application of neural network to model the low-frequency small signal response of a Gallium-Arsenide HEMT will be investigated. The third and last chapter will deal with the EM-based characterization of Gallium-Nitride transistor parasitic structures and its usage, combined with small-signal and noise measurements, for developing a transistor model ori-ented to low-noise amplifiers design. In particular, the design of a three stages low-noise amplifier with more than 20 dB of gain and less than 1.8 dB of noise figure operating in Ku-band will be described

Novel MMIC design process using waveform engineering

It has always been the case that talented individuals with an innate understanding of their subject have been able to produce works of outstanding performance. The purpose of engineering science is to define ways in which such achievements can be made on a regular,predictable basis with a high degree of confidence in success. Some tools, such as computers, have enabled an increase in speed and accuracy, whilst others have given a dramatic increase in the insight into the operation or behavior of materials; the electron microscope for instance. Still others have enabled the creation of devices on a scale unimaginable to our predecessors, Molecular Beam Epitaxy for example. This work is the product of the availability of an understanding of complex theory on microwave transistor operation, significant increases in mathematical processing and data handling, and the assembly of a ‘tool’ that not only allows the measurement of high frequency waveforms, but their manipulation to simultaneously create the environments envisioned by the design engineer. It extends the operation of previous narrow band active load pull measurement systems to 40GHz and importantly facilitates the design of high efficiency modes at X band. The main tenant of this work is to propose that rather than the linear approach of characterisation, design, test, re-iterate, that has been the standard approach to MMIC design to date, the first three stages should be integrated into a single approach which should obviate the need for design reiteration. The result of this approach should be better performance from amplifier designs, greater probability of success first time, and lower costs through less wafer real estate being consumed and fewer sign ‘spins’

Gallium Nitride Integrated Microsystems for Radio Frequency Applications.

The focus of this work is design, fabrication, and characterization of novel and advanced electro-acoustic devices and integrated micro/nano systems based on Gallium Nitride (GaN). Looking beyond silicon (Si), compound semiconductors, such as GaN have significantly improved the performance of the existing electronic devices, as well as enabled completely novel micro/nano systems. GaN is of particular interest in the “More than Moore” era because it combines the advantages of a wide-band gap semiconductor with strong piezoelectric properties. Popular in optoelectronics, high-power and high-frequency applications, the added piezoelectric feature, extends the research horizons of GaN to diverse scientific and multi-disciplinary fields. In this work, we have incorporated GaN micro-electro-mechanical systems (MEMS) and acoustic resonators to the GaN baseline process and used high electron mobility transistors (HEMTs) to actuate, sense and amplify the acoustic waves based on depletion, piezoelectric, thermal and piezo-resistive mechanisms and achieved resonance frequencies ranging from 100s of MHz up to 10 GHz with frequency×quality factor (f×Q) values as high as 1013. Such high-performance integrated systems can be utilized in radio frequency (RF) and microwave communication and extreme-environment applications.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135799/1/azadans_1.pd

Analysis and Design of a Sub-THz Ultra-Wideband Phased-Array Transmitter

This thesis investigates circuits and systems for broadband high datarate transmitter systems in the millimeter-wave (mm-wave) spectrum. During the course of this dissertation, the design process and characterization of a power efficient and wideband binary phase-shift keying (BPSK) transmitter integrated circuit (IC) with local oscillator (LO) frequency multiplication and 360° phase control for beam steering is studied. All required circuit blocks are designed based on the theoretical analysis of the underlying principles, optimized, fabricated and characterized in the research laboratory targeting low power consumption, high efficiency and broadband operation. The phase-controlled push-push (PCPP) architecture enabling frequency multiplication by four in a single stage is analytically studied and characterized finding an optimum between output power and second harmonic suppression depending on the input amplitude. A PCPP based LO chain is designed. A circuit is fabricated establishing the feasibility of this architecture for operation at more than 200 GHz. Building on this, a second circuit is designed, which produces among the highest saturated output powers at 2 dBm. At less than 100 mW of direct current (DC) power consumption, this results in a power-added efficiency (PAE) of 1.6 % improving the state of the art by almost 30 %. Phase-delayed and time-delayed approaches to beam steering are analyzed, identifying and discussing design challenges like area consumption, signal attenuation and beam squint. A 60 GHz active vector-sum phase-shifter with high gain of 11.3 dB and output power of 5 dBm, improving the PAE of the state of the art by a factor of 30 achieving 6.29 %, is designed. The high gain is possible due to an optimization of the orthogonal signal creation stage enabled by studying and comparing different architectures leading to a trade off of lower signal attenuation for higher area consumption in the chosen electromagnetic coupler. By combining this with a frequency quadrupler, a phase steering enabled LO chain for operation at 220 GHz is created and characterized, confirming the preceding analysis of the phase-frequency relation during multiplication. It achieves a power gain of 21 dB, outperforming comparable designs by 25 dB. This allows the combination of phase control, frequency multiplication and pre-amplification. The radio frequency (RF) efficiency is increased 40-fold to 0.99 %, with a total power consumption of 105 mW. Motivated by the distorting effect of beam squint in phase-delayed broadband array systems, a novel analog hybrid beam steering architecture is devised, combining phase-delayed and time-delayed steering with the goal of reducing the beam squint of phase-delayed systems and large area consumption of time-delayed circuits. An analytical design procedure is presented leading to the research finding of a beam squint reduction potential of more than 83 % in an ideal system. Here, the increase in area consumption is outweighed by the reduction in beam squint. An IC with a low power consumption of 4.3 mW has been fabricated and characterized featuring the first time delay circuit operating at above 200 GHz. By producing most of the beam direction by means of time delay the beam squinting can be reduced by more than 75 % in measurements while the subsequent phase shifter ensures continuous beam direction control. Together, the required silicon area can be reduced to 43 % compared to timedelayed systems in the same frequency range. Based on studies of the optimum signal feeding and input matching of a Gilbert cell, an ultra-wideband, low-power mixer was designed. A bandwidth of more than 100 GHz was achieved exceeding the state of the art by 23 %. With a conversion gain of –13 dB, this enables datarates of more than 100 Gbps in BPSK operation. The findings are consolidated in an integrated transmitter operating around 246 GHz doubling the highest published measured datarates of transmitters with LO chain and power amplifier in BPSK operation to 56 Gbps. The resulting transmitter efficiency of 7.4 pJ/bit improves the state of the art by 70 % and 50 % over BPSK and quadrature phaseshift keying (QPSK) systems, respectively. Together, the results of this work form the basis for low-power and efficient next-generation wireless applications operating at many times the datarates available today.:Abstract 3 Zusammenfassung 5 List of Symbols 11 List of Acronyms 17 Prior Publications 19 1. Introduction 21 1.1. Motivation........................... 21 1.2. Objective of this Thesis ................... 25 1.3. Structure of this Thesis ................... 27 2. Overview of Employed Technologies and Techniques 29 2.1. IntegratedCircuitTechnology................ 29 2.2. Transmission Lines and Passive Structures . . . . . . . . 35 2.3. DigitalModulation ...................... 41 3. Frequency Quadrupler 45 3.1. Theoretical Analysis of Frequency Multiplication Circuits 45 3.2. Phase-Controlled Push-Push Principle for Frequency Quadrupling.......................... 49 3.3. Stand-alone Phase-Controlled Push-Push Quadrupler . 60 3.4. Phase-Controlled Push-Push Quadrupler based LO-chain with High Output Power ............... 72 9 4. Array Systems and Dynamic Beam Steering 91 4.1. Theoretical Analysis of BeamSteering. . . . . . . . . . . 95 4.2. Local Oscillator Phase Shifting with Vector-Modulator PhaseShifters......................... 107 4.3. Hybrid True-Time and Phase-Delayed Beam Steering . 131 5. Ultra-Wide Band Modulator for BPSK Operation 155 6. Broadband BPSK Transmitter System for Datarates up to 56 Gbps 167 6.1. System Architecture ..................... 168 6.2. Measurement Technique and Results . . . . . . . . . . . 171 6.3. Summary and performance comparison . . . . . . . . . 185 7. Conclusion and Outlook 189 A. Appendix 195 Bibliography 199 List of Figures 227 Note of Thanks 239 Curriculum Vitae 241Diese Dissertation untersucht Schaltungen und Systeme für breitbandige Transmittersysteme mit hoher Datenrate im Millimeterwellen (mm-wave) Spektrum. Im Rahmen dieser Arbeit werden der Entwurfsprozess und die Charakterisierung eines leistungseffizienten und breitbandigen integrierten Senders basierend auf binärer Phasenumtastung (BPSK) mit Frequenzvervielfachung des Lokaloszillatorsignals und 360°-Phasenkontrolle zur Strahlsteuerung untersucht. Alle erforderlichen Schaltungsblöcke werden auf Grundlage von theoretischen Analysen der zugrundeliegenden Prinzipien entworfen, optimiert, hergestellt und im Forschungslabor charakterisiert, mit den Zielen einer niedrigen Leistungsaufnahme, eines hohen Wirkungsgrades und einer möglichst großen Bandbreite. Die phasengesteuerte Push-Push (PCPP)-Architektur, welche eine Frequenzvervierfachung in einer einzigen Stufe ermöglicht, wird analytisch untersucht und charakterisiert. Dabei wird ein Optimum zwischen Ausgangsleistung und Unterdrückung der zweiten Harmonischen des Eingangssignals in Abhängigkeit von der Eingangsamplitude gefunden. Es wird eine LO-Kette auf PCPP-Basis entworfen. Eine Schaltung wird präsentiert, die die Machbarkeit dieser Architektur für den Betrieb bei mehr als 200 GHz nachweist. Darauf aufbauend wird eine zweite Schaltung entworfen, die mit 2 dBm eine der höchsten publizierten gesättigten Ausgangsleistungen erzeugt. Mit einer Leistungsaufnahme von weniger als 100mW ergibt sich ein Leistungswirkungsgrad (PAE) von 1.6 %, was den Stand der Technik um fast 30 % verbessert. Es werden phasenverzögerte und zeitverzögerte Ansätze zur Steuerung der Strahlrichtung analysiert, wobei Entwicklungsherausforderungen wie Flächenverbrauch, Signaldämpfung und Strahlschielen identifiziert und diskutiert werden. Ein aktiver Vektorsummen-Phasenschieber mit hoher Verstärkung von 11.3 dB und einer Ausgangsleistung von 5 dBm, der mit einer PAE von 6.29 % den Stand der Technik um den Faktor 30 verbessert, wird entworfen. Die hohe Verstärkung ist zum Teil auf eine Optimierung der orthogonalen Signalerzeugungsstufe zurückzuführen, die durch die Untersuchung und den Vergleich verschiedener Architekturen ermöglicht wird. Bei der Entscheidung für einen elektromagnetischen Koppler rechtfertigt die geringere Signaldämpfung einen höheren Flächenverbrauch. Durch die Kombination mit einem Frequenzvervierfacher wird eine LO-Kette mit Phasensteuerung für den Betrieb bei 220 GHz geschaffen und charakterisiert, was die vorangegangene Analyse der Phasen-FrequenzBeziehung während der Multiplikation bestätigt. Sie erreicht einen Leistungsgewinn von 21 dB und übertrifft damit vergleichbare Designs um 25dB. Dies ermöglicht die Kombination von Phasensteuerung, Frequenzvervielfachung und Vorverstärkung. Der HochfrequenzWirkungsgrad wird um das 40-fache auf 0.99 % bei einer Gesamtleistungsaufnahme von 105 mW gesteigert. Motiviert durch den verzerrenden Effekt des Strahlenschielens in phasengesteuerten Breitbandarraysystemen, wird eine neuartige analoge hybride Strahlsteuerungsarchitektur untersucht, die phasenverzögerte und zeitverzögerte Steuerung kombiniert. Damit wird sowohl das Strahlenschielen phasenverzögerter Systeme als auch der große Flächenverbrauch zeitverzögerter Schaltungen reduziert. Es wird ein analytisches Entwurfsverfahren vorgestellt, das zu dem Forschungsergebnis führt, dass in einem idealen System ein Potenzial zur Reduktion des Strahlenschielens von mehr als 83 % besteht. Dabei wird die Zunahme des Flächenverbrauchs durch die Verringerung des Strahlenschielens aufgewogen. Es wird ein IC mit einer geringen Leistungsaufnahme von 4.3mW hergestellt und charakterisiert. Dabei wird die erste Zeitverzögerungsschaltung entworfen, die bei über 200 GHz arbeitet. Durch die Erzeugung eines Großteils der Strahlrichtung mittels Zeitverzögerung kann das Schielen des Strahls bei Messungen um mehr als 75% reduziert werden, während der nachfolgende Phasenschieber eine kontinuierliche Steuerung der Strahlrichtung gewährleistet. Insgesamt kann die benötigte Siliziumfläche im Vergleich zu zeitverzögerten Systemen im gleichen Frequenzbereich auf 43 % reduziert werden. Auf der Grundlage von Studien zur optimalen Signaleinspeisung und Eingangsanpassung einer Gilbert-Zelle wird ein Ultrabreitband-Mischer mit geringem Stromverbrauch entworfen. Dieser erreicht eine Ausgangsbandbreite von mehr als 100 GHz, die den Stand der Technik um 23% übertrifft. Bei einer Wandlungsverstärkung von –13dB ermöglicht dies Datenraten von mehr als 100 Gbps im BPSK-Betrieb. Die Erkenntnisse werden in einem integrierten, breitbandigen Sender konsolidiert, der um 246 GHz arbeitet und die höchsten veröffentlichten gemessenen Datenraten für Sender mit LO-Signalkette und Leistungsverstärker im BPSK-Betrieb auf 56 Gbps verdoppelt. Die daraus resultierende Transmitter-Effizienz von 7.4 pJ/bit verbessert den Stand der Technik um 70 % bzw. 50 % gegenüber BPSKund Quadratur Phasenumtastung (QPSK)-Systemen. Zusammen bilden die Ergebnisse dieser Arbeit die Grundlage für stromsparende, effiziente, mobile Funkanwendungen der nächsten Generation mit einem Vielfachen der heute verfügbaren Datenraten.:Abstract 3 Zusammenfassung 5 List of Symbols 11 List of Acronyms 17 Prior Publications 19 1. Introduction 21 1.1. Motivation........................... 21 1.2. Objective of this Thesis ................... 25 1.3. Structure of this Thesis ................... 27 2. Overview of Employed Technologies and Techniques 29 2.1. IntegratedCircuitTechnology................ 29 2.2. Transmission Lines and Passive Structures . . . . . . . . 35 2.3. DigitalModulation ...................... 41 3. Frequency Quadrupler 45 3.1. Theoretical Analysis of Frequency Multiplication Circuits 45 3.2. Phase-Controlled Push-Push Principle for Frequency Quadrupling.......................... 49 3.3. Stand-alone Phase-Controlled Push-Push Quadrupler . 60 3.4. Phase-Controlled Push-Push Quadrupler based LO-chain with High Output Power ............... 72 9 4. Array Systems and Dynamic Beam Steering 91 4.1. Theoretical Analysis of BeamSteering. . . . . . . . . . . 95 4.2. Local Oscillator Phase Shifting with Vector-Modulator PhaseShifters......................... 107 4.3. Hybrid True-Time and Phase-Delayed Beam Steering . 131 5. Ultra-Wide Band Modulator for BPSK Operation 155 6. Broadband BPSK Transmitter System for Datarates up to 56 Gbps 167 6.1. System Architecture ..................... 168 6.2. Measurement Technique and Results . . . . . . . . . . . 171 6.3. Summary and performance comparison . . . . . . . . . 185 7. Conclusion and Outlook 189 A. Appendix 195 Bibliography 199 List of Figures 227 Note of Thanks 239 Curriculum Vitae 24

Study of the III-nitride materials grown by mixed-source HVPE for white LED applications emitting multi spectrum range

The purpose of this study is to explore the possibility of phosphor-free white-emitting LED？s based in the gallium nitride material system. The structures are to be grown using mixed source hydride vapor phase epitaxy (MS-HVPE). It is unique crystal growth technology different from conventional HVPE and MOCVD system using mixed metal source of aluminum, indium and gallium. The first step in this project is the optimization of MS-HVPE growth process. This was achieved successfully, as binary, ternary and quaternary films are demonstrated. Successful n and p-type doping are also demonstrated introducing Te and Mg. The second step in this project is fabricating broadband spectrum emitting device of phosphor-free white LED by MS-HVPE. The device structure consisted of conventional double-hetero (DH) structure, which was the undoped InAlGaN active layer and n, p-AlGaN cladding layers. We observed that the device of AlInGaN quarternary active grown by MS-HVPE emitted multi spectrum from UV to red area. We also found that its spectrum was variable as indium mole fraction and controllable. It was nano phase epitaxy phenomenon being only observed in HS-HVPE process. An extensive growth study of GaN based material was also carried out. The effects of several growth parameters on emission characteristics were presented. PL emission wavelengths for each structure were demonstrated. And EL emission wavelengths were also demonstrated after wafer fabrication process. Additionally, x-ray diffraction and x-ray photoelectron spectroscopy (XPS) showed to verify crystal quality of MS-HVPE. The dissertation presented herein demonstrates achieving phosphor-free solid-state white lighting. But it still has unknown physical characteristics. Continuation of this study will lead to future industry. And hopefully it will be commercialized and applied to residential illumination due to this technology.Chapter 1. Introduction 1 1.1. Overview of LED 1 1.2. Wide bandgap compound semiconductor 6 1.3. Overview of white LED 10 1.4. Purpose and outline of this project 15 Chapter 2. Fundamentals of Gallium Nitride 21 2.1. Introduction 21 2.1.1. Current Issues in GaN-based LED 23 2.2. Crystallography of Gallium Nitride 26 2.3. Characteristics of Gallium Nitride 32 2.3.1. Doping of Gallium Nitride 33 2.3.2. Optical Properties of Gallium Nitride 35 2.3.3. Polarity in Gallium Nitride 38 2.4. Substrates for GaN Epitxial Growth 40 2.4.1. Substrate issues 40 2.4.2. Sapphire 41 2.4.3. SiC 45 Chapter 3. Overview of Epitaxial Growth Experimental 57 3.1. Hydride vapor phase epitaxy 57 3.1.1. Introduction to HVPE 57 3.1.2. Mixed source HVPE system 59 3.1.3. Some parameters for optimized GaN growth 62 3.2. Wafer fabrication process 63 3.2.1. Selective area growth 63 3.2.2.Metallization of GaN 64 3.3. Measurements 66 3.3.1. Photoluminescence 66 3.3.2. DXRD 67 3.3.3. SEM/CL 70 3.3.4. E-CV 75 3.3.5. Hall measurement 77 Chapter 4. Mixed Source HVPE Growth Experiment for Bulk Characteristics 82 4.1. GaN growth 82 4.1.1 Buffer growth for GaN layer 83 4.1.2. Mg-doped GaN layer 87 4.2. AlGaN growth 90 4.3. InGaN growth 97 Chapter 5. Fabrication of AlInGaN-Based LED for White Emission 115 5.1. AlInGaN SAG-DH structure growth 115 5.2. Characterization of AlInGaN SAG-DH epitaxial structure 123 5.3. Device fabrication 127 Chapter 6. Experimental Results for Active layer’s Condition 135 6.1. Performance of AlInGaN white LED 136 6.2. EL characteristics of AlGaN and AlInGaN active 139 6.2.1 GaN active layer 139 6.2.2 Al(0.1g)GaN active layer 141 6.2.3 Al(0.3g)GaN active layer 144 6.2.4 Al(0.4g)GaN active layer 144 6.2.5 Al(0.5g)GaN active layer 146 6.2.6 Al(0.6g)GaN active layer 149 6.2.7 In(0.1g) Al(0.6g) GaN active layer 151 6.2.8 In(0.2g)Al(0.6g)GaN active layer 153 6.2.9 In(0.3g)Al(0.6g)GaN active layer 155 6.2.10 In(0.4g)Al(0.6g)GaN active layer 158 6.2.11 In(0.5g)Al(0.6g)GaN active layer 160 6.3. XRD characteristics 163 Chapter 7. Phosphor &#8211Free White LED Lamp 180 7.1. Manufacturing of white LED lamp 180 7.2. Analysis of White LED Spectra and Color Rendering 181 7.3. Measurement of Phospohor free white LED 189 7.4. Future research 197 Chapter 8. Conclusions 200 Publications 202 Conference 204 Biography 209 Acknowledgements 21

Modelação não-linear de transistores de potência para RF e microondas

Doutoramento em Engenharia Electrotécnic