Engineering Commons^™

Data Center Power System Emulation And Gan-Based High-Efficiency Rectifier With Reactive Power Regulation, Jingjing Sun

Doctoral Dissertations

Data centers are indispensable for today's computing and networking society, which has a considerable power consumption and significant impact on power system. Meanwhile, the average energy usage efficiency of data centers is still not high, leading to significant power loss and system cost.

In this dissertation, effective methods are proposed to investigate the data center load characteristics, improve data center power usage efficiency, and reduce the system cost.

First, a dynamic power model of a typical data center ac power system is proposed, which is complete and able to predict the data center's dynamic performance. Also, a converter-based data center …

Investigating Operational Modes In Gallium Nitride Photoconductive Switches, Brad J. Maynard

Electrical and Computer Engineering ETDs

As switching requirements for speed, power, and efficiency become more stringent, advances in wide-bandgap (WBG) materials has enabled their use in high power switching devices. One such device, the photoconductive semiconductor switch (PCSS), while previously constructed from GaAs, shows promise using WBG Mn-doped GaN. Lateral and vertical geometries of PCSS have been produced and evaluated for operation using sub-mJ/ns regime pulsed laser incidence. At fields below 25 kV/cm, the lateral switch operates in the linear regime where modest photocurrent fitting the laser envelope is observed. Above this threshold, the switches demonstrate circuit-limited persistent conductivity (PC) current, in what is presumed …

Dc-Dc Buck Boost Converter Using The Lt8390 Controller And Gan High Electron Mobility Transistors, Juan Manuel Urbano Jr, Brian Thongchai Keokot

Electrical Engineering

California Polytechnic State University, San Luis Obispo’s ongoing Energy Harvesting from Exercise Machines (EHFEM) project creates a sustainable energy source by converting physical exercise from exercise machines into renewable electricity. Implementing energy harvesting technology into the Recreation Center’s exercise machines helps Cal Poly make progress on its goal of carbon neutrality by 2050 [1]. An improvement to the system with new technology increases Cal Poly Recreation Center’s ability to save money and improve sustainability.

The focus of this project improves the design of Nicholas Serres, who used the LT8390 controller in his buck boost DC-DC converter [2]. This project improves …

Optical Engineering Of Iii-Nitride Nanowire Light-Emitting Diodes And Applications, Ha Quoc Thang Bui

Dissertations

Applications of III-nitride nanowires are intensively explored in different emerging technologies including light-emitting diodes (LEDs), laser diodes, photodiodes, biosensors, and solar cells. The synthesis of the III-nitride nanowires by molecular beam epitaxy (MBE) is investigated with significant achievements. III-nitride nanowires can be grown on dissimilar substrates i.e., silicon with nearly dislocation free due to the effective strain relaxation. III-nitride nanowires, therefore, are perfectly suited for high performance light emitters for cost-effective fabrication of the advanced photonic-electronic integrated platforms. This dissertation addresses the design, fabrication, and characterization of III-nitride nanowire full-color micro-LED (µLED) on silicon substrates for µLED display technologies, high-efficient …

Etched-And-Regrown Diodes On M-Plane Gan For Next Generation Power Electronic Devices, Andrew A. Aragon

Electrical and Computer Engineering ETDs

Demand for next-generation power electronic devices is driven by continually evolving requirements of power systems. Devices utilizing III-nitride materials (GaN) and vertical selective-area doped architectures are advantageous due to their wide- bandgap, thermal management, small form-factor, and current handling.

Such devices incorporate junctions at multiple crystalline planes. Thus, effects of impurity contamination and etch damage are investigated on the m-plane (10-10) of GaN. Impurites (Si, O, and C) are shown to reduce blocking voltage (~ 10² ×) and increase forward leakage current (~ 10⁴ ×) in regrown versus continuously-grown p-n diodes. Elevated deep level defects at Ec – …

Nonpolar Gan-Based Vcsels With Lattice-Matched Nanoporous Distributed Bragg Reflector Mirrors, Saadat M. Mishkat-Ul-Masabih

Electrical and Computer Engineering ETDs

Wide-bandgap optoelectronic devices have undergone significant advancements with the advent of commercial light-emitting diodes and edge-emitting lasers in the violet-blue spectral region. They are now ubiquitous in several lighting, communication, data storage, display, and sensing applications. Among the III-nitride emitters, vertical-cavity surface-emitting lasers (VCSELs) have attracted significant attention in recent years due to their inherent advantages over edge-emitting lasers. The small active volume enables single-mode operation with low threshold currents and high modulation bandwidths. Their surface-normal device geometry is conducive to the cost-effective formation of high-density 2D arrays while simplifying on-chip wafer testing. Furthermore, the low beam divergence and circular …

Dc-Dc Converter For Electric Vehicle, Jason Y. Zhou, Nicholas James Mah

Electrical Engineering

In this work, a DC-DC converter is designed for an electric vehicle. The DC-DC converter is designed to provide 500W with a 200-400V input and a 12-15V adjustable output. Electric vehicle sales are beginning to increase in popularity and the need for DC-DC converters to siphon power from the tractive system is not yet fully satisfied, especially for single-seater class vehicles. Additionally, improving performance in efficiency without sacrificing wide input voltage range can benefit future DC-DC converter designs. In the end, a forward active clamp DC-DC converter is designed and tested. Additionally, spreadsheet calculators, LTSpice simulations, and Matlab scripts were …

Characterization Of Hydride Vapor Phase Epitaxy Grown Gan Substrates For Future Iii-Nitride Growth, Alaa Ahmad Kawagy

Graduate Theses and Dissertations

The aim of this research is to investigate and characterize the quality of commercially obtained gallium nitride (GaN) on sapphire substrates that have been grown using hydride vapor phase epitaxy (HVPE). GaN substrates are the best choice for optoelectronic applications because of their physical and electrical properties. Even though HVPE GaN substrates are available at low-cost and create the opportunities for growth and production, these substrates suffer from large macro-scale defects on the surface of the substrate.

In this research, four GaN on sapphire substrates were investigated in order to characterize the surface defects and, subsequently, understand their influence on …

Highly Efficient Gan-Based Single-Phase Transformer-Less Pv Grid-Tied Inverter, Khaled Alatawi

Electronic Theses and Dissertations

Growing energy demand and environmental concerns have led to an increased interest in renewable energy resources to provide a sustainable and low carbon emission energy supply. Among these renewable energy resources, photovoltaic (PV) systems have been the focus of many scientific researchers. The most vital component of a PV system that needs to be improved is the power converter. Grid-tied transformer-less inverters have gained a lot of interest in recent years because of their higher efficiency, reduced volume and lower cost compared to traditional line transformer inverters.

This dissertation discusses single-phase transformer-less inverter challenges and provides solutions that could lead …

Characterization Of Gallium Nitride Photoconductive Semiconductor Switches In The Nonlinear Regime, Joseph D. Teague

Electrical and Computer Engineering ETDs

The energy demands of an increasingly electrified world have caused a renewed interest in once dormant fields of research. Photoconductive Semiconductor switches (PCSS) are one of these fields. They theoretically offer high voltage, high current switching in sub cm³ packaging, without the shot to shot variation and bulk of current high-power DC switches such as spark gaps. PCSS are capable of power densities of 10⁹-10¹⁰ W/cm³, with electric fields ranging from 10⁵-10⁶ V/cm and current densities from 10⁴-10⁶ A/cm² [1].

Most PCSS make a trade-off between voltage, …

Review And Characterization Of Gallium Nitride Power Devices, Edward Andrew Jones

Masters Theses

Gallium Nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This thesis reviews the characteristics and commercial status of both vertical and lateral GaN power devices from the user perspective, providing the background necessary to understand the significance of these recent developments. Additionally, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, …

Beyond Conventional C-Plane Gan-Based Light Emitting Diodes: A Systematic Exploration Of Leds On Semi-Polar Orientations, Morteza Monavarian

Theses and Dissertations

Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the “Green Gap”, is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the “quantum confined Stark effect”) and low indium incorporation efficiency that …

Simulation Of Gan Based Mis Varactor, Bojidha Babu

Theses and Dissertations

This work deals with novel microwave switches based on III-Nitride varactors. RF switches, power limiters and other control devices are important components of various RF systems, such as wireless modules of laptops, tablets, cell phones etc., satellites communication systems, radars, multi-band wireless and aerospace communications, phased array antennas and so worth. Traditional RF switches are fabricated using pin diodes or MEMS, Si MOSFETs or GaAs HEMTs. These devices have a number of fundamental limitations. Si or GaAs based devices suffer from a low breakdown voltage and cannot handle high RF power. Pin-diodes require large forward currents and do not allow …

Energy-Efficient And Power-Dense Dc-Dc Converters In Data Center And Electric Vehicle Applications Using Wide Bandgap Devices, Weimin Zhang

Doctoral Dissertations

The ever increasing demands in the energy conversion market propel power converters towards high efficiency and high power density. With fast development of data processing capability in the data center, the server will include more processors, memories, chipsets and hard drives than ever, which requires more efficient and compact power converters. Meanwhile, the energy-efficient and power-dense converters for the electric vehicle also result in longer driving range as well as more passengers and cargo capacities. DC-DC converters are indispensable power stages for both applications. In order to address the efficiency and density requirements of the DC-DC converters in these applications, …

Gallium Nitride: Analysis Of Physical Properties And Performance In High-Frequency Power Electronic Circuits, Dalvir K. Saini

Browse all Theses and Dissertations

Gallium nitride (GaN) technology is being adopted in a variety of power electronic applications due to their high efficiencies even at high switching speeds. In comparison with the silicon (Si) transistors, the GaN-based devices exhibit lower on-state resistance and parasitic capacitances. The thermal performance of the GaN transistors are also better than the Si counterparts due to their higher junction temperature and lower temperature-coefficient of on-resistance. These unique properties make the gallium-nitride power transistors an appropriate selection for power electronic converters and radio-frequency power amplifiers, where size, efficiency, power density, and dynamic performance are major requirements.

Foreseeing the immense capabilities …

Development Of Micro-Hall Devices For Current Sensing, Thomas White

Graduate Theses and Dissertations

In this work, micro-Hall devices were developed for the purpose of sensing current within a high temperature and high power environment. GaAs HEMT, InGaAs pHEMT, and GaN HEMT structures were studied. These structures were grown by molecular beam epitaxy. Processing techniques including photolithography, metallization, Si deposition, wet etching, and dry etching were studied. Electrical characterization measurements including low frequency noise, Hall effect, sensitivity, capacitance-voltage, and current-voltage were performed.

Electron mobility and sheet carrier density studies were performed for both the InGaAs pHEMT and GaAs HEMT structures. Results indicated the InGaAs pHEMT was superior and thus fabricated as the micro-Hall device. …

An Analytical And Experimental Biosensor For Human Mig Using Algan/Gan Based Hemt Devices, Hector Trevino Ii

Theses and Dissertations - UTB/UTPA

An amperometric biosensor using AlGaN/GaN based HEMT devices is constructed experimentally and validated through analytical and numerical techniques for detection of a key protein in allograft rejection (Human MIG/CXCL9). The prototype developed provides a reliable sensing platform that will allow label-free and marker-free detection. By exploiting characteristics unique to AlGaN/GaN based HEMT devices, a floating gate configuration is employed to allow reliable sensing without the need for any reference electrode. Self-assembled monolayers (SAM) are formed at the gate surface by using a crosslinker (DSP) to allow for appropriate immobilization of target antibodies. A theoretical analytical and numerical model is developed …

Investigation Of Degradation Effects Due To Gate Stress In Gan-On-Si High Electron Mobility Transistors Through Analysis Of Low Frequency Noise, Michael Curtis Meyer Masuda

Master's Theses

Gallium Nitride (GaN) high electron mobility transistors (HEMT) have superior performance characteristics compared to Silicon (Si) and Gallium Arsenide (GaAs) based transistors. GaN is a wide bandgap semiconductor which allows it to operate at higher breakdown voltages and power. Unlike traditional semiconductor devices, the GaN HEMT channel region is undoped and relies on the piezoelectric effect created at the GaN and Aluminum Gallium Nitride (AlGaN) heterojunction to create a conduction channel in the form of a quantum well known as the two dimensional electron gas (2DEG). Because the GaN HEMTs are undoped, these devices have higher electron mobility crucial for …

Optical Characterization Of Ingan Heterostructures For Blue Light Emitters And Vertical Cavity Lasers: Efficiency And Recombination Dynamics, Serdal Okur

Theses and Dissertations

OPTICAL CHARACTERIZATION OF INGAN HETEROSTRUCTURES FOR BLUE LIGHT EMITTERS AND VERTICAL CAVITY LASERS: EFFICIENCY AND RECOMBINATION DYNAMICS

By Serdal Okur, Ph.D.

A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University.

Virginia Commonwealth University, 2014.

Major Director: Ümit Özgür, Associate Professor, Electrical and Computer Engineering

This thesis explores radiative efficiencies and recombination dynamics in InGaN-based heterostructures and their applications as active regions in blue light emitters and particularly vertical cavities. The investigations focus on understanding the mechanism of efficiency loss at high injection as well as developing designs to mitigate …

Quantum Efficiency Enhancement For Gan Based Light-Emitting Diodes And Vertical Cavity Surface-Emitting Lasers, Fan Zhang

Theses and Dissertations

This thesis explores the improvement of quantum efficiencies for InGaN/GaN heterostructures and their applications in light-emitting diodes (LEDs) and vertical cavity surface-emitting lasers (VCSELs). Different growth approaches and structural designs were investigated to identify and address the major factors limiting the efficiency. (1) Hot electron overflow and asymmetrical electron/hole injection were found to be the dominant reasons for efficiency degradation in nitride LEDs at high injection; (2) delta p-doped InGaN quantum barriers were employed to improve hole concentration inside the active region and therefore improve hole injection without sacrificing the layer quality; (3) InGaN active regions based on InGaN multiple …

Enhancing Gan Led Efficiency Through Nano-Gratings And Standing Wave Analysis, Gabriel M. Halpin

Master's Theses

Improving energy efficient lighting is a necessary step in reducing energy consumption.Lighting currently consumes 17% of all U.S. residential and commercial electricity, but a report from the U.S. Office of Energy Efficiency and Renewable Energy projects that switching to LED lighting over the next 20 years will save 46% of electricity used in lighting.GaN LEDs are used for their efficient conversion of electricity to light, but improving GaN efficiency requires optically engineering the chip to extract more light.Total internal reflection limits GaN LED performance since light must approach the chip surface within 23.6° of normal to escape into air.This thesis …

Dc, Rf, And Thermal Characterization Of High Electric Field Induced Degradation Mechanisms In Gan-On-Si High Electron Mobility Transistors, Matthew Anthony Bloom

Master's Theses

Gallium Nitride (GaN) high electron mobility transistors (HEMTs) are becoming increasingly popular in power amplifier systems as an alternative to bulkier vacuum tube technologies. GaN offers advantages over other III-V semiconductor heterostructures such as a large bandgap energy, a low dielectric constant, and a high critical breakdown field. The aforementioned qualities make GaN a prime candidate for high-power and radiation-hardened applications using a smaller form-factor. Several different types of semiconductor substrates have been considered for their thermal properties and cost-effectiveness, and Silicon (Si) has been of increasing interest due to a balance between both factors.

In this thesis, the DC, …

Frequency Characterization Of Si, Sic, And Gan Mosfets Using Buck Converter In Ccm As An Application, Keshava Gopalakrishna

Browse all Theses and Dissertations

Present day applications using power electronic converters are focusing towards improving the speed, efficiency, and robustness. This led to the implementation of new devices in such converters where speed and efficiency are of concern. As silicon (Si) based power devices are approaching their operational performance limits with respect to speed, it is essential to analyze the properties of new devices, which are capable of replacing silicon based devices. Wide band-gap (WBG) semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) are such materials, whose material properties show promising advantages for power electronic applications.

This thesis focuses on the …

Light Extraction Enhancement Of Gan Based Leds Using Top Gratings, Patterned Sapphire Substrates, And Reflective Surfaces, Greg Chavoor

Master's Theses

In the last 15 years, an immense amount of research has gone into developing high efficiency Gallium Nitride based light emitting diodes (LED). These devices have become increasingly popular in LED displays and solid state lighting. Due to the large difference in refractive index between GaN and Air, a significant amount of light reflects at the boundary and does not escape the device. This drawback decreases external quantum efficiency (EQE) by minimizing light extraction. Scientists and engineers continue to develop creative solutions to enhance light extraction. Some solutions include surface roughening, patterned sapphire substrates, and reflective layers.

This study proposes …

Growth And Characterization Of Non-Polar Gan Materials And Investigation Of Efficiency Droop In Ingan Light Emitting Diodes, Xianfeng Ni

Theses and Dissertations

General lighting with InGaN light emitting diodes (LEDs) as light sources is of particular interest in terms of energy savings and related environmental benefits due to high lighting efficiency, long lifetime, and Hg-free nature. Incandescent and fluorescent light sources are used for general lighting almost everywhere. But their lighting efficiency is very limited: only 20-30 lm/W for incandescent lighting bulb, approximately 100 lm/W for fluorescent lighting. State-of-the-art InGaN LEDs with a luminous efficacy of over 200 lm/W at room temperature have been reported. However, the goal of replacing the incandescent and fluorescent lights with InGaN LEDs is still elusive since …

Enhanced Light Extraction Efficiency From Gan Light Emitting Diodes Using Photonic Crystal Grating Structures, Simeon S. Trieu

Master's Theses

Gallium nitride (GaN) light emitting diodes (LED) embody a large field of research that aims to replace inefficient, conventional light sources with LEDs that have lower power, higher luminosity, and longer lifetime. This thesis presents an international collaboration effort between the State Key Laboratory for Mesoscopic Physics in Peking University (PKU) of Beijing, China and the Electrical Engineering Department of California Polytechnic State University, San Luis Obispo. Over the course of 2 years, Cal Poly’s side has simulated GaN LEDs within the pure blue wavelength spectrum (460nm), focusing specifically on the effects of reflection gratings, transmission gratings, top and bottom …

Tuning Of Electrical Properties In Inaln/Gan Hfets And Ba0.5sr0.5tio3/Yig Phase Shifters, Jacob H. Leach

Theses and Dissertations

Engineers know well from an early point in their training the trials and tribulations of having to make design tradeoffs in order to optimize one performance parameter for another. Discovering tradeoff conditions that result in the elimination of a loss associated with the enhancement of some other parameter (an improvement over a typical tradeoff), therefore, ushers in a new paradigm of design in which the constraints which are typical of the task at hand are alleviated. We call such a design paradigm “tuning” as opposed to “trading off”, and this is the central theme of this work. We investigate two …

Gan Heterojunction Fet Device Fabrication, Characterization And Modeling, Qian Fan

Theses and Dissertations

This dissertation is focused on the research efforts to develop the growth, processing, and modeling technologies for GaN-based Heterojunction Field Effect Transistors (HFETs). The interest in investigating GaN HFETs is motivated by the advantageous material properties of nitride semiconductor such as large band gap, large breakdown voltage, and high saturation velocity, which make it very promising for the high power and microwave applications. Although enormous progress has been made on GaN transistors in the past decades, the technologies for nitride transistors are still not mature, especially concerning the reliability and stability of the device. In order to improve the device …

Optimization Of Gan Laser Diodes Using 1d And 2d Optical Simulations, Sean Richard Keali'i Jobe

Master's Theses

This paper studies the optical properties of a GaN Laser Diode (LD). Through simulation, the GaN LD is optimized for the best optical confinement factor. It is found that there are optimal thicknesses of each layer in the diode that yield the highest optical confinement factor. There is a strong relationship between the optical confinement factor and lasing threshold—a higher optical confinement factor results in a lower lasing threshold. Increasing optical confinement improves lasing efficiency. Blue LDs are important to the future of lighting sources as they represent the final color in the RGB spectrum that does not have a …

Low Dislocation Density Gallium Nitride Templates And Their Device Applications, Jinqiao Xie

Theses and Dissertations

The unique properties, such as large direct bandgap, excellent thermal stability, high μH × ns, of III-nitrides make them ideal candidates for both optoelectronic and high-speed electronic devices. In the past decades, great success has been achieved in commercialization of GaN based light emitting diodes (LEDs) and laser diodes (LDs). However, due to the lack of native substrates, thin films grown on sapphire or SiC substrates have high defect densities that degrade the device performance and reliability. Conventional epitaxy lateral overgrowth (ELO) can reduce dislocation densities down to ∼10-6 cm-2 in the lateral growth area, but requires ex situ photolithography …