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Title:On the generation, dissipation, and transport of heat in GaN materials for advanced high-power devices
Author(s):Park, Kihoon
Director of Research:Bayram, Can
Doctoral Committee Chair(s):Bayram, Can
Doctoral Committee Member(s):Leburton, Jean-Pierre; Lyding, Joseph; Sinha, Sanjiv
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
gallium nitride
thermal conductivity
thermal resistance
Abstract:GaN semiconductors show excellent optical and electronic properties such as large direct bandgap (3.4 eV), high breakdown field (3.3 MV/cm), high saturation velocity (2.5×107 cm/s), and high thermal stability. However, many GaN-based devices that rely on the material’s capacity to flow high current and sustain high voltage levels suffer from undesirable Joule heating effects that critically limit their performance and device lifetime. Thermal management, therefore, has become essential in applications such as high-brightness light-emitting diodes and AlGaN/GaN-based high-electron-mobility transistors (HEMTs). An accurate understanding of the thermal properties in GaN material is crucial to improve the reliability and performance of GaN-based high-power devices. This work addresses the generation, dissipation, and transport of heat in GaN materials and devices. First, the interactions between electrons and optical phonons are investigated to understand the intrinsic electronic and phonon properties in GaN-based structures. Based on the theoretical uniaxial dielectric continuum model, a formalism is developed to calculate the electron mobility and saturation velocity as a function of temperature. It is found that at room temperature, the phonon-limited mobility is ~3000 cm2/V-s (with a power law of T-3.1) and saturation velocity is ~3.1×107 cm/s. Furthermore, properties of interface and confined optical phonons and their interactions with electrons are studied in an AlN/GaN/AlN quantum well structure. Next, the heat dissipation in GaN/substrate stacks is analyzed using TCAD software to understand the relation between the thermal resistance, thermal boundary resistance (of GaN/substrate interface), and GaN thickness. As commercially available bulk GaN is extremely expensive, cost-driven consumer electronics applications are mostly implemented on GaN grown on foreign substrates. The effects of these substrates on thermal resistance of GaN devices are investigated considering multiple design parameters. We propose a device design scheme that can be used to optimize the GaN layer thickness and minimize the device thermal resistance assuming an isotropic heat dissipation from the hotspot located under the drain side of the gate. Finally, the dislocation density dependent thermal conductivity of GaN is experimentally investigated using techniques such as cathodoluminescence, X-ray diffraction, secondary ion mass spectroscopy, and time-domain thermoreflectance. Four types of GaN samples (hydride vapor phase epitaxy grown GaN, high nitrogen pressure grown GaN, metal-organic chemical vapor deposition grown GaN on sapphire and silicon) are studied to understand the relationship between dislocation density and thermal conductivity. A systematic analysis of the various experimental setup variables of the technique is also performed to optimize the measurement of GaN thermal conductivity.
Issue Date:2020-01-31
Rights Information:© 2020 Kihoon Park
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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