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1
Li, Ting. "Gallium nitride and aluminum gallium nitride-based ultraviolet photodetectors /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Muensit, Supasarote. "Piezoelectric coefficients of gallium arsenide, gallium nitride and aluminium nitride." Phd thesis, Australia : Macquarie University, 1999. http://hdl.handle.net/1959.14/36187.
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"1998"--T.p.Thesis (PhD)--Macquarie University, School of Mathematics, Physics, Computing and Electronics, 1999.
Includes bibliographical references.
Introduction -- A Michelson interferometer for measurement of piezoelectric coefficients -- The piezoelectric coefficient of gallium arsenide -- Extensional piezoelectric coefficients of gallium nitrides and aluminium nitride -- Shear piezoelectric coefficients of gallium nitride and aluminium nitride -- Electrostriction in gallium nitride, aluminium nitride and gallium arsenide -- Summary and prognosis.
The present work represents the first use of the interferometric technique for determining the magnitude and sign of the piezoelectric coefficients of III-V compound semiconductors, in particular gallium arsenide (GaAs), gallium nitride (GaN), and aluminium nitride (AIN). The interferometer arrangement used in the present work was a Michelson interferometer, with the capability of achieving a resolution of 10⁻¹³ m. -- The samples used were of two types. The first were commercial wafers, with single crystal orientation. Both GaAs and GaN were obtained in this form. The second type of sample was polycrystalline thin films, grown in the semiconductor research laboratories at Macquarie University. GaN and AIN samples of this type were obtained. -- The d₁₄ coefficient of GaAs was measured by first measuring the d₃₃ value of a [111] oriented sample. This was then transformed to give the d₁₄ coefficient of the usual [001] oriented crystal. The value obtained for d₁₄ was (-2.7 ± 0.1) pmV⁻¹. This compares well with the most recent reported measurements of -2.69 pmV⁻¹. The significance of the measurement is that this represents the first time this coefficient has been measured using the inverse piezoelectric effect. -- For AIN and GaN samples, the present work also represents the first time their piezoelectric coefficients have been measured by interferometry. For GaN, this work presents the first reported measurements of the piezoelectric coefficients, and some of these results have recently been published by the (Muensit and Guy, 1998). The d₃₃ and d₃₁ coefficients for GaN were found to be (3.4 ± 0.1) pmV⁻¹ and (-1.7 ± 0.1) pmV⁻¹ respectively. Since these values were measured on a single crystal wafer and have been corrected for substrate clamping, the values should be a good measure of the true piezoelectric coefficients for bulk GaN. -- For AIN, the d₃₃ and d₃₁ coefficients were found to be (5.1 ± 0.2) pmV⁻¹, and (-2.6 ± 0.1) pmV⁻¹ respectively. Since these figures are measured on a polycrystalline sample it is quite probable that the values for bulk AIN would be somewhat higher.
The piezoelectric measurements indicate that the positive c axis in the nitride films points away from the substrate. The piezoelectric measurements provide a simple means for identifying the positive c axis direction. -- The interferometric technique has also been used to measure the shear piezoelectric coefficient d₁₅ for AIN and GaN. This work represents the first application of this technique to measure this particular coefficient. The d₁₅ coefficients for AIN and GaN were found to be (-3.6 ± 0.1) pmV⁻¹ and (-3.1 ± 0.1) pmV⁻¹ respectively. The value for AIN agrees reasonably well with the only reported value available in the literature of -4.08 pmV⁻¹. The value of this coefficient for GaN has not been measured. -- Some initial investigations into the phenomenon of electrostriction in the compound semiconductors were also performed. It appears that these materials have both a piezoelectric response and a significant electrostrictive response. For the polycrystalline GaN and AIN, the values of the M₃₃ coefficients are of the order of 10⁻¹⁸ m²V⁻². The commercial single crystal GaN and GaAs wafers display an asymmetric response which cannot be explained.
Mode of access: World Wide Web.
Various pagings ill
3
Mareš, Petr. "Depozice Ga a GaN nanostruktur na křemíkový a grafenový substrát." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231443.
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Presented thesis is focused on the study of properties of Ga and GaN nanostructures on graphene. In the theoretical part of the thesis a problematics of graphene and GaN fabrication is discussed with a focus on the relation of Ga and GaN to graphene. The experimental part of the thesis deals with the depositions of Ga on transferred CVD-graphene on SiO2. The samples are analyzed by various methods (XPS, AFM, SEM, Raman spectroscopy, EDX). The properties of Ga on graphene are discussed with a focus on the surface enhanced Raman scattering effect. Furthermore, a deposition of Ga on exfoliated graphene and on graphene on a copper foil is described. GaN is fabricated by nitridation of the Ga structures on graphene. This process is illustrated by the XPS measurements of a distinct Ga peak and the graphene valence band during the process of nitridation.
4
Cheng, Chung-choi, and 鄭仲材. "Positron beam studies of fluorine implanted gallium nitride and aluminium gallium nitride." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43278577.
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Cheng, Chung-choi. "Positron beam studies of fluorine implanted gallium nitride and aluminium gallium nitride." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43278577.
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Popa, Laura C. "Gallium nitride MEMS resonators." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99296.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 187-206).
As a wide band-gap semiconductor, with large breakdown fields and saturation velocities, Gallium Nitride (GaN) has been increasingly used in high-power, high-frequency electronics and monolithic microwave integrated circuits (MMICs). At the same time, GaN also has excellent electromechanical properties, such as high acoustic velocities and low elastic losses. Together with a strong piezoelectric coupling, these qualities make GaN ideal for RF MEMS resonators. Hence, GaN technology offers a platform for the seamless integration of low-loss, piezoelectric RF MEMS resonators with high power, high frequency electronics. Monolithic integration of MEMS resonators with ICs would lead to reduced parasitics and matching constraints, enabling high-purity clocks and frequency-selective filters for signal processing and high-frequency wireless communications. This thesis highlights the physics and resonator design considerations that must be taken into account in a monolithically integrated solution. We then show devices that achieve the highest frequency-quality factor product in GaN resonators to date (1.56 x 1013). We also highlight several unique transduction mechanisms enabled by this technology, such as the ability to use the 2D electron gas (2DEG) channel of High Electron Mobility Transistors (HEMTs) as an electrode for transduction. This enables a unique out-of-line switching capability which allowed us to demonstrate the first DC switchable solid-state piezoelectric resonator. Finally, we discuss the benefits of using active HEMT sensing of the mechanical signal when scaling to GHz frequencies, which enabled the highest frequency lithographically defined resonance reported to date in GaN (3.5 GHz). These demonstrated features sh
by Laura C. Popa.
Ph. D.
7
Allums, Kimberly K. "Proton radiation and thermal stabilty [sic] of gallium nitride and gallium nitride devices." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013123.
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Holmes, Kenneth L. "Two-dimensional modeling of aluminum gallium nitride/gallium nitride high electron mobility transistor." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Jun%5FHolmes.pdf.
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Anderson, David Richard. "Phonon-limited electron transport in gallium nitride and gallium nitride-based heterostructures, 1760-1851." Thesis, University of York, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270104.
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Jackson, Helen C. "Effect of variation of silicon nitride passivation layer on electron irradiated aluminum gallium nitride/gallium nitride HEMT structures." Thesis, Air Force Institute of Technology, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3629786.
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Silicon nitride passivation on AlGaN\GaN heterojunction devices can improve performance by reducing electron traps at the surface. This research studies the effect of displacement damage caused by 1 MeV electron irradiation as a function of the variation of passivation layer thickness and heterostructure layer variation on AlGaN/GaN HEMTs. The effects of passivation layer thickness are investigated at thicknesses of 0, 20, 50 and 120 nanometers on AlGaN\GaN test structures with either an AlN nucleation layer or a GaN cap structures which are then measured before and immediately after 1.0 MeV electron irradiation at fluences of 1016 cm-2. Hall system measurements are used to observe changes in mobility, carrier concentration and conductivity as a function of Si3N4 thickness. Models are developed that relate the device structure and passivation layer under 1 MeV radiation to the observed changes to the measured photoluminescence and deep level transient spectroscopy. A software model is developed to determine the production rate of defects from primary 1 MeV electrons that can be used for other energies and materials. The presence of either a 50 or 120 nm Si 3N4 passivation layer preserves the channel current for both and appears to be optimal for radiation hardness.
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Wang, Siping S. M. Massachusetts Institute of Technology. "Gallium Nitride phononic crystal resonator." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99831.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 41-42).
We present a Gallium Nitride (GaN) Lamb Wave resonator using a Phononic Crystal (PnC) to selectively confine elastic vibrations with wide-band spurious mode suppression. A unique feature of the design demonstrated here is a folded PnC structure to relax energy confinement in the non-resonant dimension and to enable routing access of piezoelectric transducers inside the resonant cavity. This provides a clean spectrum over a wide frequency range and improves series resistance relative to transmission line or tethered resonators by allowing a low-impedance path for drive and sense electrodes. GaN resonators are demonstrated with wide-band suppression of spurious modes, f -Q product up to 3.06 x 1012, and resonator coupling coefficient k2.eff up to 0.23%. (filter BW up to 0.46%). Furthermore, these PnC GaN resonators exhibit record-breaking power handling, with IIP3 of +27.2dBm demonstrated at 993MHz.
by Siping Wang.
S.M.
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Zhang, Anping. "Gallium nitride-based electronic devices." [Gainesville, Fla.] : University of Florida, 2001. http://etd.fcla.edu/etd/uf/2001/anp1299/Title.PDF.
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Thesis (Ph. D.)--University of Florida, 2001.Title from first page of PDF file. Document formatted into pages; contains vii, 145 p.; also contains graphics. Vita. Includes bibliographical references (p. 137-144).
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Deatcher, Christopher J. "Growth and characterisation of gallium nitride and indium gallium nitride by MOVPE for photonic applications." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400334.
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Hoy, Daniel R. "Gallium Nitride and Aluminum Gallium Nitride Heterojunctions for Electronic Spin Injection and Magnetic Gadolinium Doping." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331855661.
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Mußer, Markus [Verfasser], and Oliver [Akademischer Betreuer] Ambacher. "Micro-System: Gallium Nitride RF-Broad-Band High-Power Amplifier = Mikrosystem: Gallium Nitride HF Breitband Hochleistungsverstärker." Freiburg : Universität, 2015. http://d-nb.info/1123482640/34.
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Shih, Andy. "Resonant tunneling in gallium nitride and aluminum nitride nanowire heterostructures." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117124.
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III-V gallium nitride and aluminum nitride semiconductor nanowire heterostructures have emerged as promising candidates for numerous photonic device applications, ranging from the visible to the near-, mid- and far-infrared spectral range. In this work, the electrical properties of gallium nitride and aluminum nitride nanowire heterostructures were studied in the context of resonant tunneling. The negative differential resistance was observed in current-voltage measurements at room temperature and at 77 K for single nanowire devices as well as for large area devices, confirming the presence of resonant tunneling through the aluminum nitride barriers. Effects of different silicon doping profiles have also been discussed. This work represents a preliminary step in developing gallium nitride and nanowire based intersubband devices such as quantum cascade lasers and infrared-based photodetectors.Les nanofils semi-conducteurs hétérostructurés composés de nitrure de gallium et d'aluminium III-V ont émergé comme des candidats prometteurs pour de nombreuses applications de dispositifs photoniques, allant de la lumière visible à l'infrarouge proche, moyen et lointain. Dans ce projet, les propriétés électriques et l'effet tunnel résonnant de nanofils semi-conducteurs hétérostructurés de nitrure de gallium et d'aluminium ont été étudiés. La résistance différentielle négative a été observée dans les mesures de courant-tension à la température ambiante et à 77 K pour les dispositifs à un seul nanofil ainsi que des dispositifs de grande surface avec plusieurs nanofils, ce qui confirme la présence d'effet tunnel résonnant à travers les barrières de nitrure d'aluminium. Les effets des différents profils de dopage de silicium ont également été discutés. Ce travail représente une étape préliminaire dans le développement des appareils intersousbandes de nanofils de nitrure de gallium tels que les lasers à cascade quantique et photodétecteurs infrarouge.
17
Ho, Kwok-Lun. "Metalorganic chemical vapor deposition of aluminum nitride and gallium nitride." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13142.
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Hess, Stefan. "Time-resolved spectroscopy of gallium nitride." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301575.
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MartiÌnez, Charles E. "Phonon interactions in gallium nitride nanostructures." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430567.
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Piedra, Daniel Ph D. Massachusetts Institute of Technology. "Development of gallium nitride power transistors." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/66454.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2011."November 2010." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 78-79).
GaN-based high-voltage transistors have outstanding properties for the development of ultra-high efficiency and compact power electronics. This thesis describes a new process technology for the fabrication of GaN power devices optimized for their use in efficient power distribution systems in computer micro-processors. An existing process flow was used to fabricate the baseline single-finger transistors and additional process steps were developed and optimized to fabricate multi-finger devices with total gate widths up to 12mm. These transistors offer the current and on-resistance levels required by future GaN-based power converters. Transistors with various gate widths were fabricated and characterized by DC and capacitancevoltage measurements to study how the main transistor metrics scale with gate width.
by Daniel Piedra.
M.Eng.
21
Yoon, Joonah. "Electronic properties of gallium nitride nanowires." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45438.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.Includes bibliographical references (leaves 123-131).
This thesis presents a systematic study of the electrical transport in GaN nanowires. Particularly, the effect of the surrounding dielectric on the conductivity of GaN nanowires is experimentally shown for the first time. Our GaN nanowires are grown by catalytic vapor growth methods, specifically hydride vapor phase epitaxy (HVPE) and chemical vapor deposition (CVD). TEM and XRD studies indicate that both of our HVPE and CVD grown GaN nanowires have the wurtzite single crystal structure. The crystal orientations along the wire axis are (1000) and (1010) for our HVPE and CVD grown nanowires, respectively. The mean diameters are 200 nm and 46 nm for the HVPE and the CVD grown nanowires, respectively. CVD GaN nanowires with three different surrounding configurations are prepared to study the effect of the surrounding dielectric. The GaN nanowires are either laid directly on a SiO2/Si substrate, or freely suspended between metal contacts, or embedded in SiO2. The conductivity is measured as a function of temperature, nanowire diameter, and the surrounding dielectric. The donor ionization energies are extracted from the temperature dependence of the conductivity. In all cases, two sets of the activation energies are obtained. One set of these activation energies shows an inverse dependence on nanowire radius and the other set is found to be independent of the radius. The inverse radius dependence of the activation energy is explained by the polarization charges, which are induced by the donor ions, at the interface between the nanowires and their surroundings. This so-called dielectric confinement is found to have a substantial effect, more than the quantum confinement effect, for GaN nanowires with diameter larger than 10 nm or so. The radius-independent activation energy is found to be due to the impurity band conduction near the surface. We also successfully fabricated nanowire field-effect transistors (FETs) using both HVPE and CVD grown GaN nanowires. For the thinnest CVD grown nanowires, complete control of the carrier density was achieved. The field-effect mobility of the CVD grown GaN nanowires is estimated to be - 18 cm2/V.s, which is more than an order of magnitude smaller than that of the bulk GaN.
(cont.) A redshift of the near-bandedge emission in the room-temperature photoluminescence measurements of the CVD grown GaN indicates a high impurity concentration. The metallic approximation using a capacitor model shows the carrier density to be - 4 x 1019cm-3. Reduction of the background impurities is expected to decrease the scattering from the ionized impurities and to improve the carrier mobility and switching behavior of the nanowire FETs.
by Joonah Yoon.
Ph.D.
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Zhu, Tongtong. "Nanoscale electrical characterization of gallium nitride." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609346.
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Owsley, Jack Lee III. "CHARACTERIZATION OF DOPED GALLIUM NITRIDE SUBSTRATES." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1357763392.
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Shankar, Ramya. "Charge transport in gallium nitride nanowires." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0025011.
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Maffeis, Thierry Gabriel Georges. "Formation of metal-gallium nitride contacts." Thesis, Sheffield Hallam University, 2001. http://shura.shu.ac.uk/19998/.
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The influence of pre-metallisation surface preparation on the structural, chemical, and electrical properties of metal-nGaN interfaces has been investigated by X-ray Photoemission Spectroscopy (XPS), current-voltage measurement (I-V) and cross section Transmission Electron Microscopy (TEM). XPS analysis showed that the three GaN substrate treatments investigated, ex-situ HF etch, in-situ anneal in Ultra-High-Vacuum (UHV), and in-situ Ga reflux cleaning in UHV result in surfaces increasingly free of contaminants. Additionally, the three treatments are found to induce increasingly larger upward band bending. Ag-nGaN contacts formed after Ga reflux cleaning exhibit a Schottky barrier height of 0.80 eV and an ideality factor of 1.56, as determined by I-V.XPS and TEM characterisation of Au-nGaN formed after the three pre-metallisation surface treatments show that HF etching and UHV annealing produce abrupt, well-defined interfaces. Conversely, GaN substrate cleaning in a Ga flux results in Au/GaN intermixing. I-V characterisation of Au-nGaN contacts yield a Schottky barrier height of 1.25 eV with very low ideality factor and very good contact uniformity for the pre-metallisation UHV anneal while the Ga reflux cleaning result in a much lower barrier (0.85 eV), with poor ideality and uniformity. I-V and XPS results suggest a high density of acceptor states at the surface, which is further enhanced by UHV annealing. The mechanisms of Ga-nGaN, Ag-nGaN and Au-nGaN Schottky barrier formation are discussed in the context of the Metal-Induced Gap States model (MIGS) Unified Defect Model (UDM) and Cowley-Sze model.
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Stevens, Lorin E. "Thermo-Piezo-Electro-Mechanical Simulation of AlGaN (Aluminum Gallium Nitride) / GaN (Gallium Nitride) High Electron Mobility Transistor." DigitalCommons@USU, 2013. http://digitalcommons.usu.edu/etd/1506.
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Due to the current public demand of faster, more powerful, and more reliable electronic devices, research is prolific these days in the area of high electron mobility transistor (HEMT) devices. This is because of their usefulness in RF (radio frequency) and microwave power amplifier applications including microwave vacuum tubes, cellular and personal communications services, and widespread broadband access. Although electrical transistor research has been ongoing since its inception in 1947, the transistor itself continues to evolve and improve much in part because of the many driven researchers and scientists throughout the world who are pushing the limits of what modern electronic devices can do. The purpose of the research outlined in this paper was to better understand the mechanical stresses and strains that are present in a hybrid AlGaN (Aluminum Gallium Nitride) / GaN (Gallium Nitride) HEMT, while under electrically-active conditions. One of the main issues currently being researched in these devices is their reliability, or their consistent ability to function properly, when subjected to high-power conditions. The researchers of this mechanical study have performed a static (i.e. frequency-independent) reliability analysis using powerful multiphysics computer modeling/simulation to get a better idea of what can cause failure in these devices. Because HEMT transistors are so small (micro/nano-sized), obtaining experimental measurements of stresses and strains during the active operation of these devices is extremely challenging. Physical mechanisms that cause stress/strain in these structures include thermo-structural phenomena due to mismatch in both coefficient of thermal expansion (CTE) and mechanical stiffness between different materials, as well as stress/strain caused by "piezoelectric" effects (i.e. mechanical deformation caused by an electric field, and conversely voltage induced by mechanical stress) in the AlGaN and GaN device portions (both piezoelectric materials). This piezoelectric effect can be triggered by voltage applied to the device's gate contact and the existence of an HEMT-unique "two-dimensional electron gas" (2DEG) at the GaN-AlGaN interface. COMSOL Multiphysics computer software has been utilized to create a finite element (i.e. piece-by-piece) simulation to visualize both temperature and stress/strain distributions that can occur in the device, by coupling together (i.e. solving simultaneously) the thermal, electrical, structural, and piezoelectric effects inherent in the device. The 2DEG has been modeled not with the typically-used self-consistent quantum physics analytical equations, rather as a combined localized heat source* (thermal) and surface charge density* (electrical) boundary condition. Critical values of stress/strain and their respective locations in the device have been identified. Failure locations have been estimated based on the critical values of stress and strain, and compared with reports in literature. The knowledge of the overall stress/strain distribution has assisted in determining the likely device failure mechanisms and possible mitigation approaches. The contribution and interaction of individual stress mechanisms including piezoelectric effects and thermal expansion caused by device self-heating (i.e. fast-moving electrons causing heat) have been quantified. * Values taken from results of experimental studies in literature
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Baghani, Erfan. "Electrical properties of dislocations within the nitride based semiconductors gallium nitride and indium nitride." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43581.
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Dislocation lines affect the electrical and optical
properties of semiconductors. In this research, the effect that the threading dislocation lines have on the free electron concentration and the electron mobility within gallium nitride and indium nitride is investigated. A formulation is developed for
obtaining the screening space charge concentration
and the corresponding electrostatic potential profile surrounding the dislocation lines. The resultant electrostatic potential profile has
then been used to compute the associated electron mobility, limited by scattering from the charged
dislocation lines. As part of this research, a Gibbs factor formalism is also developed that can readily obtain the occupation statistics of the defect sites associated with the threading dislocation lines.
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Cai, Xingmin. "Growth, doping and nanostructures of gallium nitride." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B35806394.
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Cai, Xingmin, and 蔡興民. "Growth, doping and nanostructures of gallium nitride." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B35806394.
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Winser, Andrew James. "Photoluminescence studies of arsenic-doped gallium nitride." Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405387.
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Flannery, Lorraine Barbara. "Electrical and optoelectronic properties of gallium nitride." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268478.
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CALDAS, PAULA GALVAO. "NANOSCALE MECHANICAL DEFORMATION MECHANISMS OF GALLIUM NITRIDE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25364@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
Neste trabalho foi estudada a deformação mecânica em filmes de GaN por nanoindentação. Um nanoindentador foi usado para induzir a nucleação de defeitos mecânicos na superfície das amostras de forma controlada. A morfologia das indentações e a microestrutura dos defeitos foram estudados com o uso da microscopia de força atômica e microscopia eletrônica de transmissão . Os resultados mostraram que nos estágios iniciais de deformação, o processo de nanoindentação promove o escorregamento em escala atômica de planos cristalinos que pode ser revertido se a carga é removida. Se a carga for aumentada ainda mais, a partir de uma tensão crítica, ocorre um grande evento pop-in com o escorregamento dos planos 1101, 1122 e 0001 produzindo então deformação plástica irreversível. A influência dos dopantes na deformação mecânica foi estudada e os resultados mostraram que é mais difícil produzir deformação mecânica em filmes de GaN dopado com Si e dopado com Mg do que no filme não dopado. A autorrecuperação que ocorre após a retirada da ponta foi estudada utilizando cristais de ZnO com diferentes orientações. O mecanismo de ativação térmica dos loops de discordância foi estudado através da observação da influência da temperatura no processo de autorrecuperação parcial dos cristais. Medidas de catodoluminescência foram usadas para identificar as distribuições de tensão associadas à deformação plástica permanente mostrando que esta induz regiões de tensão trativa ao longo das direções a 1120 nos filmes de GaN dopado e não dopado.
In this work, the mechanical deformation of GaN films was studied by nanoindentation. A nanoindenter was used to induce the nucleation of mechanical defects on the samples surfaces in a controlled manner. The morphology of the indentations and the microstructure of the defects were studied using atomic force microscopy and transmission electron microscopy. The results showed that in the early stages of deformation, the nanoindentation process promotes slip at the atomic scale of the pyramidal planes of the crystal that can be reversed if the load is removed. If load is further increased, locking of these atomic plains occur leading to a hardened crystal region. It acts as an extension of the tip of the indenter redistributing the applied stress. At a critical stress, a major pop-in event occurs with the slip of the 1101, 1122 and 0001 plains leading then to irreversible plastic deformation. The influence of doping on the mechanical deformation has been studied and the results showed that it is more difficult to produce mechanical deformation in GaN films doped with Si and Mg doped than in undoped films. The self-recovery that occurs after removal of the tip was investigated using ZnO crystals with different orientations. The mechanism of thermal activation of dislocation loops was studied by observing the influence of temperature on the self-recovery process of the crystals. Cathodoluminescence measures were used to identify the resulting stress distributions associated with permanent plastic deformation showing that this induces tensile regions along the a 1120 directions in doped and undoped GaN films.
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Hari, Nikita. "Gallium nitride power electronics using machine learning." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288610.
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Gallium Nitride (GaN) power devices have the potential to jump-start the next generation of power converters which are smaller, faster, denser, and cheaper. They are thus expected to meet the increasing 21st Century need for power density and efficiency, while at the same time reducing pollution. With the commercialisation of 600 V GaN power devices, which the industry is keen to adopt, come significant challenges. Since there are a number of such devices which are new to the power community, there is a steep learning curve involved, with dispersed information on how best to employ these devices. This work aims to solve this problem through the development of a universal GaN power device and circuit model and the formulation of design rules and guidelines. Through this contribution, designers will be able to better understand and work with these novel devices with relative ease. This will aid the need for faster adoption of GaN devices by the industry solving the barriers to commercialisation. This research demonstrates the use of machine learning (ML) algorithms for behavioural modelling of GaN power devices. Introducing ML as the key to developing a general behavioural and circuit model for GaN power devices combined with understanding, learning, customizing and successfully demonstrating it is the major contribution of this research work. This research first presents a comprehensive investigation into the parasitic effect on the GaN device switching performance. A simple process based on RF techniques is introduced to approximately extract the impedances of the GaN device to develop a behavioural model. The switching behaviour of the model is validated using simulation and double pulse test experiments at 450 V, 10 A test conditions. The developed behavioural model for Transhporm GaN HEMT is 95.2% accurate as the existing LT-spice manufacturer model, and is very much easier for power designers to handle, without the need for knowledge about the physics or geometry of the device. However, given that separate models would need to be developed for each commercial GaN device, the need for a generalized and accurate GaN behavioural model was identified, and it is this generalised model that the remainder of this thesis focuses on. In the next part of this research, a GaN platform test bench is built through bridging RF and power electronics design methodologies to achieve a gate loop and power loop inductance of around 1.8nH with switching waveforms with rise time and fall time around 2.5ns at 450V, 15A, 500KHz test conditions. The double pulse test circuits are customized using different off the shelf gate drives and analysed for collecting switching data for training the ML model. ML modelling using supervised learning is used to predict the switching voltage and current waveforms thus making it possible to construct a generic GaN black box model. Different architectures with single and multi- layer neural networks are explored for modelling. The ability to demonstrate a GaN device ML model that maps both voltage and current inputs and outputs is another characteristic and novel feature of this work. This research demonstrates different types of GaN ML models. The developed voltage and current prediction models are based on feed forward neural network (FFNN), long short-term memory unit (LSTM) and gated recurrent unit (GRU). Several parameters are quantified and compared for validating the models. They are the network architectures, parameters, training time, validation loss and error loss. The ML models are also compared with the demonstrated model of chapter 3 and existing LT-Spice manufacturer models. The results show that the author has been able to develop a GaN LSTM ML model with an error rate of 0.03, and convergence at 3s with excellent stability. The ML based modelling is then translated from GaN power devices to GaN based circuits. Among the different neural network architectures trained and tested, a multi FFNN with 5 hidden layers and 30 neurons, was found to be the best for prediction and optimization. The switching behaviour comparison results shows the benefits and value of ML modelling in opening up whole new possibilities of employing advanced control algorithms for very efficient, reliable and scalable performance of GaN power electronics systems. Finally, the findings of this work have been generalized to frame machine learning based techniques to address the need for generic modelling of power electronic devices. These solutions are presented as an information manual to researchers, engineers and students interested in benefiting from adopting machine learning for power electronics applications.
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Yeh, Theresa (Theresa I. ). "Efficient wireless charging with gallium nitride FETs." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91881.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 74-77).
Though wireless charging is more convenient than traditional wired charging methods, it is currently less efficient. This not only wastes power but can also result in a longer charging time. Improving the efficiency of wireless charging systems is equivalent to reducing the sources of loss in the system. In this work, we focus on losses originating from the transistor. Resonant inductive wireless charging systems were designed and implemented for efficiency comparisons. We show in our experiments that replacing the traditional Silicon MOSFET with a Gallium Nitride FET can increase the overall system efficiency by 5%.
by Theresa Yeh.
M. Eng.
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Giam, Louise R. "Gallium Nitride (GaN) quantum dot layer formation." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35070.
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Sumner, Joy. "Scanning probe microscopy studies on Gallium nitride." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612451.
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Boudjelida, Boumedienne. "Metal-aluminium gallium nitride Schottky contacts formation." Thesis, Sheffield Hallam University, 2006. http://shura.shu.ac.uk/19373/.
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X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of various surface cleaning procedures on Al[x]Ga[1]-[x]N surfaces for x = 0.20 and 0.30. Results show that wet chemical etch in a HF solution followed by a 600°C in-situ annealing under ultra-high vacuum (UHV) is very effective in removing oxygen from the surface. Downward band bending of 0.87 eV and 0.99 eV also occurs between the solvents-treated and the annealed Al[x]Ga[1]-[x]N surfaces for x = 0.20 and 0.30, respectively. Increasing in-situ temperature annealing in increments of 100°C up to 600°C shows a re-ordering at the surface and subsurface with Ga and A1 moving deeper in the surface, whereas N goes to the topsurface. In addition, the Fermi level movement observed when increasing the temperature could be interpreted by the change in surface stoichiometry or by a creation of vacancies due to the ex-situ surface treatment which may, in turn, be activated/deactivated by temperature annealing. Atomic hydrogen clean (AHC) followed by 400°C in-situ UHV annealing is also found effective in removing O and C from Al[x]Ga[1]-[x]N surface (x = 0.20).The formation of Ag/Al[x]Ga[1]-[x]N (x = 0.20) and Ni/Al[x]Ga[1]-[x]N (x = 0.30) interfaces, where the substrate was subjected to HF etch followed by 600°C in-situ UHV anneal, has been studied by a combination of XPS, atomic force microscope (AFM), scanning tunneling microscope (STM) and current-voltage (I-V) measurements. XPS results suggest a layer-by-layer followed by islanding growth mode of Ag and Ni on Al[x]Ga[1]-[x]N. This is confirmed by the presence of metal islands at the metal-covered surfaces using AFM and in-situ STM. XPS investigation shows a more abrupt, well-defined Ag/Al[x]Ga[1]-[x]N interface compared to Ni/Al[x]Ga[1]-[x]N. Ag deposition on Al[x]Ga[1]-[x]N substrates causes upward band bending of 0.30 eV and 0.40 eV between the "clean" surface and the last metal deposition, for x = 0.20 and 0.30, respectively, while Ni induces downward band bending of 0.3 eV for x = 0.20. I-V measurements of Ag/Al[x]Ga[1]-[x]N (x = 0.30), where the substrate was cleaned using N[+] bombardment followed by 600°C annealing, yield a Schottky barrier height of 0.82 eV with ideality factor n = 1.21.XPS and I-V results on Ag/Al[x]Ga[1]-[x]N and Ni/Al[x]Ga[1]-[x]N are compared and discussed in terms of current models of Schottky barrier formation.
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Krishnamoorthy, Sriram. "Gallium Nitride Based Heterostructure Interband Tunnel Junctions." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1409019988.
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RUSSO, STEFANO. "Gallium nitride-based device simulation and development." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/737.
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Dalla sua prima apparizione nei primi anni novanta il nitrurio di gallio (GaN) ha suscitato parecchio interesse come materiale molto promettente sia per applicazioni di optoelettronica sia per dispositivi a microonde ad alta potenza. Durante gli ultimi quindici anni la ricerca di tutto il mondo ha fatto un grosso sforzo per realizzare queste promesse. Applicazioni optoelettronici basati su GaN sono gia' stati commercializzati, mentre per i dispositivi a microonde ad alta potenza manca poco alla commercializzazione. Si stima che il valore mondiale del mercato di dispositivi GaN nel 2009 ammontera' a 7.2 miliardi di dollari.Since its reappearance in the early 1990s gallium nitride (GaN) has been regarded as a very interesting and highly promising material system for both optical and microwave high-power electronic applications. Over the last fifteen years researchers all around the world have made great efforts in order to redeem these promises. GaN-based optical applications have first reached the stage of commercialization while microwave high-power electronics are on the verge of their commercial breakthrough. The value of the worldwide GaN device market, which at present is about $3.5 billion, is estimated to be $7.2 billion by the year 2009.
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Dvořák, Martin. "Depozice Ga a GaN ultratenkých vrstev na grafenový substrát." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-230846.
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This diploma thesis deals with preparation of graphene samples for depositions of ultrathin layers of gallium and gallium nitride. Graphene substrates were prepared by chemical vapour deposition in home-build high temperature reactor. After graphene transfer to silicon wafers, a series of chemical and thermal treatments were performed. Obtained samples were suitable for the study of growth of ultrathin layers of Ga and GaN. The growth of Ga and GaN was realized in ultra high vacuum conditions. Molecular beam epitaxy technique was used for gallium depositions together with ion source for nitridation. Obtained ultrathin layers were studied with X-ray photoelectron spectroscopy, atomic force microscopy and with scanning electron microscopy.
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Vacek, Petr. "Rozsáhlé defekty v nitridech Ga a Al." Doctoral thesis, Vysoké učení technické v Brně. CEITEC VUT, 2021. http://www.nusl.cz/ntk/nusl-447553.
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III-nitridy běžně krystalizují v hexagonální (wurtzitové) struktuře, zatímco kubická (sfaleritová) struktura je metastabilní a má pouze mírně vyšší energii. Jejich fyzikální vlastnosti jsou silně ovlivněny přítomností rozsáhlých defektů, které jsou v těchto dvou strukturách od sebe odlišné. U wurtzitových nitridů se jedná primárně o vláknové dislokace. Některé vláknové dislokace tvoří hluboké energetické stavy v zakázaném pásu, kterými ovlivňují elektrické a optoelektronické vlastnosti těchto materiálů. Oproti tomu, kubické nitridy obsahují množství vrstevných chyb, které představují lokální transformace do stabilnější wurtzitové struktury. Cílem této práce je charakterizovat rozsáhlé defekty v obou krystalových strukturách pomocí elektronové mikroskopie, mikroskopie atomárních sil a rentgenové difrakce. Prokázali jsme, že vzorky GaN/AlN a AlN s orientací (0001) rostlé na substrátu Si (111) pomocí epitaxe z organokovových sloučenin obsahují velkou hustotu vláknových dislokací. Nejčastější jsou dislokace s Burgersovým vektorem s komponentou ve směru a wurtzitové struktury, následované dislokacemi s Burgersovým vektorem s komponentou ve směru a+c, zatímco dislokace s Burgersovým vektorem s c komponentou jsou relativně vzácné. Pravděpodobný původ vláknových dislokací je diskutován v souvislosti s různými mechanismy růstu těchto vrstev. Prizmatické vrstevné chyby byly nalezeny v tenkých nukleačních vrstvách AlN, ale v tlustších vrstvách již nebyly přítomny. Na rozhraní AlN / Si byla nalezena amorfní vrstva složená ze SiNx a částečně taky z AlN. Navrhujeme, že by tato amorfní vrstva mohla hrát významnou roli při relaxaci misfitového napětí. Analýza elektrické aktivity rozsáhlých defektů v AlN byla provedena pomocí měření proudu indukovaného elektronovým svazkem. Zjistili jsme, že vláknové dislokace způsobují slabý pokles indukovaného proudu. Díky jejich vysoké hustotě a rovnoměrnému rozložení však mají větší vliv na elektrické vlastnosti, než mají V-defekty a jejich shluky. Topografické a krystalografické defekty byly studovány na nežíhaných a žíhaných nukleačních vrstvách kubického GaN deponovaných na 3C-SiC (001) / Si (001) substrátu. Velikost ostrůvků na nežíhaných vzorcích se zvyšuje s tloušťkou nukleační vrstvy a po žíhání se dále zvětšuje. Po žíhání se snižuje pokrytí substrátu u nejtenčích nukleačních vrstev v důsledku difúze a desorpce (nebo leptání atmosférou reaktoru). Vrstevné chyby nalezené ve vrstvách GaN, poblíž rozhraní se SiC, byly většinou identifikovány jako intrinsické a byly ohraničené Shockleyho parciálními dislokacemi. Jejich původ byl diskutován, jako i vliv parciálních dislokací na relaxaci misfitového napětí. Díky velkému množství vrstevných chyb byly podrobněji studovány jejich interakce. Na základě našich zjištění jsme vyvinuli teoretický model popisující anihilaci vrstevných chyb v kubických vrstvách GaN. Tento model dokáže předpovědět pokles hustoty vrstevných chyb se zvyšující se tloušťkou vrstvy.
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Ju, Wentao. "Experimental Investigation of the Epitaxial Lateral Overgrowth of Gallium Nitride and Simulation of Gallium Nitride Metalorganic Chemical Vapor Deposition Process." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1050589636.
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Harris, Brandon Eric. "Few cycle pulse laser induced damage studies of gallium oxide and gallium nitride." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556891689968541.
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Motayed, Abhishek. "Gallium nitride nanowire based electronic and optical devices." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7254.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Farrant, Luke. "Gallium nitride processing for high power microwave devices." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56118/.
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This thesis contains literature reviews relating to inductively coupled plasmas and their use in etching gallium nitride with chlorine based plasmas. The properties of gallium nitride, how these properties make gallium nitride a suitable material for high power microwave transistors and how such transistors will help improve the systems in which they might be used are also reviewed. In this thesis, a novel, non-destructive method of measurement of the conductivity of a semiconductor through measurement of the increase in the bandwidth of the resonant peak of a microwave dielectric resonator when it is brought near a semiconductor wafer is presented. Using this method the conductivity of a thin gallium nitride film is obtained and found to be within the expected range it was found to be very difficult to measure the conductivity of this gallium nitride wafer using a four-point probe, as the film was too thin. Also presented in this thesis are studies of the etch characteristics of gallium nitride and photoresist in mixed boron trichloride and chlorine plasmas generated in two Oxford Instruments inductively coupled plasma etchers (ICP 180 and 380). The ICP 380 was used to etch the mesa isolation of gallium nitride based heteroj unction field effect transistors that were fabricated at Cardiff University. A method of making the angle of the mesa sidewall acute by melting of the photoresist is presented. An acute mesa-sidewall angle facilitated the easy traverse of the mesa edge by the gate metal. Characterisations of ohmic and Schottky contacts that were fabricated as part of the effort to produce a working gallium nitride based heteroj unction field effect transistor are presented and reasons given for the failure of some of the ohmic contacts. The dc characteristics of the best transistor fabricated during the project are presented.
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Schuller, Timothy Adam. "Gallium nitride sensor devices fabrication techniques and characterisation." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549688.
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A saccharide sensor was fabricated using an AlGaN/GaN heterostructure structure and a boronic-acid containing receptor. Parallel to this, photoelectrochemical (PEC) etching of Gallium Nitride (GaN) was employed both as a nanostructuring technique and as a method of rapid dislocation density enumeration. The device fabrication techniques necessary for the development of devices based on n-type GaN and its alloys were successfully implemented. A robust photolithographic mask capable of producing a variety of transistor and sensor structures was designed and fabricated. Surface Charge Lithography (SCL) was studied and implemented as a technique for the nanostructuring of n-type GaN. In contrast to previous work (where patterns with feature sizes down to 100nm were created¹), several shortcomings of the technique were noted and subsequently investigated: a failure to achieve the intended minimum feature size; elongation of features in the direction of FIB instrument rastering; and the loss of thin features perpendicular to the rastering direction. A pattern design scheme to overcome these shortcomings was proposed along with experimental improvements expected to alleviate such issues. A novel receptor molecule employing a phenylboronic acid (BAT) was synthesised and used to functionalise an AlGaN/GaN FET device, thereby creating an electronic saccharide sensor device. The response of the sensor to a panel of saccharides (fructose, galactose and glucose) was investigated, with the order of response confirming previous findings (decreasing from fructose to galactose to glucose). The device was found to have good stability prior to failure, indicating that this type of sensor device shows a great deal of potential for wider use. PEC etching was used as a technique for determining the dislocation density in two distinct GaN on sapphire structures with thick AlN buffer layers. The SRI sample (100nm of GaN with 500nm of AlN) had a dislocation density of 1.9±O.2xl0⁹cm-², while the SH2 sample (500nm of GaN with lOOnm of AIN) had approximately twice this density, at 3.8±O.2xl0⁹cm-². The differences are thought to primarily arise from the difference in AlN thickness.
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Sanz, Dorleta Cortaberria. "Fabrication and characterisation of novel gallium nitride lasers." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445891.
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Chowdhury, Nadim. "p-Channel gallium nitride transistor on Si substrate." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120405.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references.
Gallium Nitride, a wide bandgap (3.4 eV) semiconductor, has outstanding attributes, such as, high breakdown electric field, high electron mobility, which make it suitable for applications requiring high power and high operating frequencies. These intrinsic material properties have been the major driving force to the development of high speed and high power GaN based n-channel transistors (mostly in the form of AlGaN/GaN High Electron Mobility Transistors). However, the full potential of GaN technology cannot be reached without the existence of p-channel GaN transistors. These devices are required for efficient high side switching in the converter circuits and for GaNCMOS technology. Therefore, the aim of this work is to demonstrate a GaN-CMOS compatible p-channel transistor. A stack of MOCVD grown epitaxial layers, is chosen for this work which has both 2-dimensional electron gas (2-DEG) for n-channel transistor and 2-dimensional hole gas (2-DHG) for p-channel transistor. The epitaxial layers chosen for this work are as follows, p++ - GaN (20 nm)/p-GaN (50 nm)/UID-GaN (20 nm)/Alo.25Gao. 75N (20 nm)/UID-GaN (150 nm)/GaNBuffer (3.8 ptm)/Si (1000 [mu]m). From device fabrication point of view, the difficulty of demonstrating a high performing p-channel GaN transistor can be attributed to the high source and drain contact resistances. In this thesis, we successfully improved the contact resistances through the development of optimum fabrication process, and a record contact resistivity of 4.83 x 10-6 [Omega]2 - cm 2 to p type-GaN was demonstrated. Finally, for the first time, a recessed gate p-channel GaN transistor on Si substrate was demonstrated. Direct current measurement of our fabricated devices show excellent off-state characteristics: ION/IOFF 5 , SS= 280 mV/decade and IOFF=- nA/mm. Measured on state characteristics for 2 pm channel length devices are, Ron= 1.7 k[omega]-mm as VGS=12 V, ION=- 3 .5 mA/mm at VGS=10 V and VDs=5 V. From the current-voltage and capacitance-voltage characteristics of 100 pm channel length devices, 2-DHG density and hole C, 2 mobility were found to be 2.4 x 1012 cm 2 and 11cm2/v.s , respectively.
by Nadim Chowdhury.
S.M.
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Emiroglu, Deniz. "Dislocation related defects in silicon and gallium nitride." Thesis, Sheffield Hallam University, 2007. http://shura.shu.ac.uk/19626/.
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This thesis examines the kinetics of carrier capture and emission from dislocations in silicon (Si) and gallium nitride (GaN) using deep level transient spectroscopy (DLTS) and Laplace DLTS (LDLTS).Laplace DLTS is a powerful tool in characterising point defect related emission, but until now it has not been used extensively for investigating emission from extended defects. Using LDLTS, broad DLTS peaks arising from dislocations in Si containing oxidation-induced stacking faults (OISF) were resolved into multiple emission rates. For the first time, the change in emission rates from deep levels due to the band edge modification at dislocations was evidenced by LDLTS.Silicon can be grown virtually defect free, but dislocations may be introduced in very-large scale integration (VLSI) to act as impurity gettering centres. Additionally, the interstitial oxygen inherent in Czochralski (Cz) silicon can be made to segregate to dislocation cores by specific bending and annealing conditions to increase the mechanical hardness of wafers. This process is termed dislocation locking. In this work, Cz-Si with different amounts of oxygen at dislocation cores were characterised by DLTS and LDLTS. Results show the presence of a deep level with complex capture properties. A direct correlation is observed between the DLTS peak height of this level and the amount of oxygen at the dislocation core. Laplace DLTS was used to resolve broad DLTS peaks into numerous emission rates. The fill pulse dependency tests revealed that certain emission rates are not affected by the long range Coulomb forces due to neighbouring states. This suggests that certain emission rates contained in the broad DLTS peaks may be associated with point defects which are not in the vicinity of dislocations. In comparison to silicon, the deep level characterisation of GaN using DLTS and Laplace DLTS is still in its infancy. In this work, the application of DLTS to n-type hexagonal GaN Schottky diodes has revealed a shallow donor level, a series of deep electron traps and a thermally activated metastable hole trap. The dominant deep electron level is shown to emit around room temperature. DLTS and Laplace DLTS results indicate that this level exhibits local band-bending and is likely to arise from dislocations. Laplace DLTS of electron traps has shown that the broad DLTS emission is made up of numerous emission rates. Some of these emission rates do not exhibit fill pulse dependency and could arise from point defects in the strain field of dislocations. If the sample is heated to 600K and cooled down, the subsequent DLTS spectrum displays a dominant negative peak due to hole emission. The spectrum recovers to its original state showing only electron traps if the sample is not electrically characterised for a period of several days or a week, depending on the sample. The formation of this level results in a significant drop in carrier density. It is discussed with reference to the gallium vacancy and its complexes with oxygen donors.
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Brown, Dustin Anthony. "Novel Approaches to Ferroelectric and Gallium Nitride Varactors." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1398902436.
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