Gallium nitride (GaN)-based microelectronics are one of the most exciting semiconductor technologies for high power density and high frequency electronics. The excellent electrical properties of GaN and its related alloys (high critical electric field, carrier concentration, and carrier mobility) have enabled record-breaking performance of GaN-based high electron mobility transistors (HEMTs) for radio-frequency (RF) applications. However, the very high power density in the active region of GaN HEMTs leads to significant degradation in performance as the device temperature increases. Thus, effective thermal management of GaN-based electronics is a key to enabling the technology to reach its full potential. Despite the vast amount of research into thermal issues in GaN-based electronics, including both modeling and experimental studies, there are a number of poorly understood issues. For instance, the heat source distribution in GaN HEMTs for RF applications has not been quantified nor have metrics been published for the heat flux in the near-junction region. Often, device engineers neglect the importance of thermal boundary conditions, which play a major role in shaping the temperature distribution in the device. Temperature rise in GaN HEMTs is typically modeled using computationally expensive numerical methods; analytical methods that are more computationally efficient are often quite limited. In this thesis, a literature review is given that discusses previous research in thermal issues in GaN-based electronics and that provides a perspective on the important factors to consider for thermal management. Electro-thermal modeling tools validated with test devices were used to derive quantitative information about the heat source distribution in GaN HEMTs. Both numerical and analytical thermal models were developed that provide helpful insight into the dominant factors in the formation of highly localized hotspots in the near-junction region. The Kirchhoff transformation, a technique for solving the heat conduction equation for situations in which the thermal conductivity of a material depends on temperature, was extended and applied to GaN HEMTs. The research described in this thesis provides critical information in understanding thermal issues in GaN-based electronics required to develop next generation near-junction thermal management technologies.

Thermal Management of Gallium Nitride Electronics outlines the technical approaches undertaken by leaders in the community, the challenges they have faced, and the resulting advances in the field. This book serves as a one-stop reference for compound semiconductor device researchers tasked with solving this engineering challenge for future material systems based on ultra-wide bandgap semiconductors. A number of perspectives are included, such as the growth methods of nanocrystalline diamond, the materials integration of polycrystalline diamond through wafer bonding, and the new physics of thermal transport across heterogeneous interfaces. Over the past 10 years, the book's authors have performed pioneering experiments in the integration of nanocrystalline diamond capping layers into the fabrication process of compound semiconductor devices. Significant research efforts of integrating diamond and GaN have been reported by a number of groups since then, thus resulting in active thermal management options that do not necessarily lead to performance derating to avoid self-heating during radio frequency or power switching operation of these devices. Self-heating refers to the increased channel temperature caused by increased energy transfer from electrons to the lattice at high power. This book chronicles those breakthroughs. Includes the fundamentals of thermal management of wide-bandgap semiconductors, with historical context, a review of common heating issues, thermal transport physics, and characterization methods Reviews the latest strategies to overcome heating issues through materials modeling, growth and device design strategies Touches on emerging, real-world applications for thermal management strategies in power electronics

Gallium Nitride-based (GaN-based) devices for power electronics have gained considerable momentum in recent years. Any improvement in conventional silicon-based (Si-based) devices is now incremental. The figure-of-merit for GaN is significantly higher than for Si due to GaN’s wide band-gap and high mobility, which result in high breakdown field and low on-resistance, respectively. Commercial GaN power devices are based on a lateral device topology: namely AlGaN/GaN high-electron mobility transistors (HEMTs). However, HEMTs exhibit well-known dispersion effects that lead to current collapse, increasing the dynamic ON resistance. The breakdown voltage in lateral HEMTs scale with gate-to-drain distance, which necessitates the lateral scaling up of devices to support high breakdown. Vertical topology has inherent advantages due to a buried electric field which enables dispersion-free operation and allows for vertical scaling. The present work addresses the device design, fabrication, and characterization of current-aperture vertical-electron transistors (CAVETs) for power switching application. A study of ion-implanted current-blocking layer (CBL) is used to demonstrate the potential to achieve high breakdown voltage. CAVETs with gate dielectrics show a premature breakdown of 60V due to gate dielectric failure. When the dielectric was replaced by a p-n junction, the breakdown voltage was improved to 500V by using a multiple energy-implantation scheme for the CBL. Thermal analysis of CAVETs was performed, and extracted device-thermal resistance was compared with lateral HEMTs grown on multiple substrates. GaN vertical diodes with avalanche capability were also fabricated and analyzed as potential candidates for transit-time diodes. Finally, design modifications were provided as future work to utilize the CAVET structures in RF power amplifiers.

Gallium Nitride (GaN) is a binary III/V wide band gap semiconductor used in power electronics for operations at high power densities and high speeds. GaN has excellent characteristics like high break-down voltage, high thermal conductivity, and high electron saturation velocity which have led to an intensive study and wide use of GaN in many fields. Some of these fields range from amplifiers, MMIC, laser diodes, pulsed radars and counter-IED jammers to CAT-V modules and fourth generation infrastructure base-stations. In this study package level thermal analysis and management of GaN high electron mobility transistor was carried out for determination of junction temperature and junction-case thermal resistance (Rjc). Two commercially available models were used as a reference for analysis. The sizes for both the models were 3 x 3 mm and 4 x 4 mm with host substrate SiC and Si respectively. The model considers the thickness of GaN and host substrate layers, the gate pitch, length, width, and thermal conductivity of GaN, and host substrate. The analysis is carried out on FEA software. Initially mesh sensitivity analysis was carried out to determine the best possible grid count for CFD analysis. Both the models were analyzed for steady state condition at various radio frequency power output to map the increment in the junction temperature. A parametric study is being carried out to optimize and reduce the maximum junction temperature and junction to case thermal resistance (Rjc) by providing convective air cooling and heat sink. The other part of this study includes optimization of the model using diamond as the host substrate and ceramic as mold compound material to monitor the decrease in the thermal resistance value. Comparative results in this study show the percentage reduction in the estimated Rjc value. Thermal resistance value is estimated using the below formula, Rjc = Tj - Tc / P From the results obtained a significant reduction in the estimated Rjc value was observed when compared for no flow, air flow with heat-sink, different host substrate and different mold compound material conditions. In conclusion GaN HEMT can be optimized to achieve a significant improvement in operation. This would allow operation of GaN devices at high temperature without damaging the reliability and operation life-span.

This book is based on nearly a decade of materials and electronics research at the leading research institution on the nitride topic in Europe. It is a comprehensive monograph and tutorial that will be of interest to graduate students of electrical engineering, communication engineering, and physics; to materials, device, and circuit engineers in research and industry; to all scientists with a general interest in advanced electronics.

Semiconductor spintronics is expected to lead to a new generation of transistors, lasers and integrated magnetic sensors that can be used to create ultra-low power, high speed memory, logic and photonic devices. Useful spintronic devices will need materials with practical magnetic ordering temperatures and current research points to gallium and aluminium nitride magnetic superconductors as having great potential. This book details current research into the properties of III-nitride semiconductors and their usefulness in novel devices such as spin-polarized light emitters, spin field effect transistors, integrated sensors and high temperature electronics. Written by three leading researchers in nitride semiconductors, the book provides an excellent introduction to gallium nitride technology and will be of interest to all reseachers and industrial practitioners wishing to keep up to date with developments that may lead to the next generation of transistors, lasers and integrated magnetic sensors.

As trends progress toward higher power applications in GaN-based electronic and photonic devices, the issue of self-heating becomes a prominent concern. This is especially the case for high-brightness light-emitting diodes (LEDs) and high electron mobility transistors (HEMTs), where the bulk of power dissipation occurs within a small (sub-micron) region resulting in highly localized temperature rises during operation. Monitoring these thermal effects becomes critical as they significantly affect performance, reliability, and overall device lifetime. In response to these issues, diamond grown by chemical vapor deposition (CVD) has emerged as a promising material in III-nitride thermal management as a heat-spreading substrate due to its exceptional thermal conductivity. This work is aimed toward the characterization of self-heating and thermal management technologies in GaN electronic and photonic devices and their materials. The two main components of this dissertation include assessing self-heating in these devices through direct measurement of temperature rises in high-power LEDs and GaN HEMTs and qualifying thermal management approaches through the characterization of thermal conductivity and material quality in CVD diamond and its incorporation into GaN device layers. The purpose of this work is to further the understanding of thermal effects in III-nitride materials as well as provide useful contributions to the development of future thermal management technologies in GaN device applications.