Gallium nitride (GaN) is a promising material for power electronics due to its outstanding properties, such as high critical electric field and large bandgap. Despite its superior intrinsic properties, fabrication processes and technology for vertical GaN power electronics is still not as mature as in conventional materials. This thesis covers three aspects of vertical power devices on bulk GaN to increase their reliability and performance. The first is the breakdown behavior of GaN under high electric fields. Vertical Schottky diodes with multi-finger anodes are simulated, fabricated and characterized. Evidence of impact ionization and signs of avalanche breakdown are shown. The second aspect is scalable fabrication technologies for vertical power FinFETs. Key processing stesps are refined and demonstrated on large-area devices. The final topic covered is GaN superjunction (SJ) technology in the context vertical power FinFETs. The SJ FinFET concept is first introduced then an underutilized method for p-type doping GaN is explored as an alternative to conventional p-type regrowth and ion implantation. Finally, the proposed GaN SJ FinFET is investigated with simulations. Various standard SJ parameters are optimized and a novel electric field management technique is proposed.

GaN is considered the most promising material candidate in next-generation power device applications, owing to its unique material properties, for example, bandgap, high breakdown field, and high electron mobility. Therefore, GaN power device technologies are listed as the top priority to be developed in many countries, including the United States, the European Union, Japan, and China. This book presents a comprehensive overview of GaN power device technologies, for example, material growth, property analysis, device structure design, fabrication process, reliability, failure analysis, and packaging. It provides useful information to both students and researchers in academic and related industries working on GaN power devices. GaN wafer growth technology is from Enkris Semiconductor, currently one of the leading players in commercial GaN wafers. Chapters 3 and 7, on the GaN transistor fabrication process and GaN vertical power devices, are edited by Dr. Zhihong Liu, who has been working on GaN devices for more than ten years. Chapters 2 and 5, on the characteristics of polarization effects and the original demonstration of AlGaN/GaN heterojunction field-effect transistors, are written by researchers from Southwest Jiaotong University. Chapters 6, 8, and 9, on surface passivation, reliability, and package technologies, are edited by a group of researchers from the Southern University of Science and Technology of China.

This unique new resource provides a comparative introduction to vertical Gallium Nitride (GaN) and Silicon Carbide (SiC) power devices using real commercial device data, computer, and physical models. This book uses commercial examples from recent years and presents the design features of various GaN and SiC power components and devices. Vertical verses lateral power semiconductor devices are explored, including those based on wide bandgap materials. The abstract concepts of solid state physics as they relate to solid state devices are explained with particular emphasis on power solid state devices. Details about the effects of photon recycling are presented, including an explanation of the phenomenon of the family tree of photon-recycling. This book offers in-depth coverage of bulk crystal growth of GaN, including hydride vapor-phase epitaxial (HVPE) growth, high-pressure nitrogen solution growth, sodium-flux growth, ammonothermal growth, and sublimation growth of SiC. The fabrication process, including ion implantation, diffusion, oxidation, metallization, and passivation is explained. The book provides details about metal-semiconductor contact, unipolar power diodes, and metal-insulator-semiconductor (MIS) capacitors. Bipolar power diodes, power switching devices, and edge terminations are also covered in this resource.

Gallium nitride (GaN) has gained considerable interest in the areas of power electronics and radio frequency (RF) devices in recent years due to its significantly higher material figure-of-merits (FOMs) than silicon (Si). The capability of operating faster as power switches also overwhelms another wide-bandgap contender, silicon carbide (SiC), especially for applications at ~600-1200 V level. GaN devices with a lateral topology such as high electron mobility transistors (HEMTs) have been extensively studied, while the development of vertical devices on high-quality free-standing GaN substrates is opening new opportunities towards improved power handling capability in high-power applications. There are still science and technology issues associated with GaN that limit its applications in high-power scenarios. One of the fundamental properties is its avalanche behavior, which is expected to be considered as a benchmark for the material but was rarely seen in GaN devices grown on foreign substrates, including sapphire, Si and SiC. Avalanche is observed and gaining increasing attention recently with the improvement of GaN-on-GaN substrate, especially in diodes. Several issues of GaN in high-power and high-speed applications are addressed in the present work. Edge terminations play a vital role in GaN devices targeting a high voltage range, and enable avalanche by optimizing the electric filed distribution, eliminating peak electric field at device edges. An ion-compensated moat etch structure is studied on GaN vertical p-n diodes. Parameters including moat etching depth and ion implantation dose are optimized. P-n diodes with a breakdown voltage (V[subscript BR]) of 1500 V and a specific on-state resistance (R[subscript ON,sp]) of 0.7 m[omega]·cm2 is demonstrated with the optimized structure, showing a device FOM of 3.2 GW·cm−2 and avalanche behavior. With avalanche performance as a prerequisite confirmed on vertical p-n diodes on bulk GaN substrates with dislocation density ranging from 1e4 cm−2 to 1e6 cm−2, the effect of dislocation density on device behavior, especially off-state leakage current is experimentally and studied in detail. The leakage mechanism is analyzed by considering its relationship to electric field and temperature. Lower leakage could be achieved on the substrate with 1e4 cm−2 dislocation density, with variable-range-hopping (VRH) procedure dominating low electric field range and Poole-Frenkel (PF) effect dominating the higher part, while VRH and other more trap-related processes may play more roles on the substrate with 1e6 cm−2 dislocation density. Large current capability is another factor for high-power applications. A DC current up to 50 A is successfully demonstrated on large-area p-n diodes by applying backside gold-to-gold thermal compression bonding. A successful scaling-up is achieved with essential factors studied. There have been few works on the RF performance of GaN vertical devices though the lateral RF devices have been widely explored. To study RF properties of GaN vertical devices, a Silvaco TCAD simulation model is established for nitride (N)-polar GaN current aperture vertical electron transistor (CAVET) based on a fitting of N-polar lateral HEMT experimental results. DC and RF properties of an N-polar CAVET are simulated, and a maximum output power of 15 W·mm−1 is expected. To experimentally demonstrate RF characteristics of a CAVET, the 1st-generation RF CAVET is then built on gallium (Ga)-polar substrate. Based on the DC characteristics, a current gain cutoff frequency (fT) at ~13 GHz is expected.

This book presents the first comprehensive overview of the properties and fabrication methods of GaN-based power transistors, with contributions from the most active research groups in the field. It describes how gallium nitride has emerged as an excellent material for the fabrication of power transistors; thanks to the high energy gap, high breakdown field, and saturation velocity of GaN, these devices can reach breakdown voltages beyond the kV range, and very high switching frequencies, thus being suitable for application in power conversion systems. Based on GaN, switching-mode power converters with efficiency in excess of 99 % have been already demonstrated, thus clearing the way for massive adoption of GaN transistors in the power conversion market. This is expected to have important advantages at both the environmental and economic level, since power conversion losses account for 10 % of global electricity consumption. The first part of the book describes the properties and advantages of gallium nitride compared to conventional semiconductor materials. The second part of the book describes the techniques used for device fabrication, and the methods for GaN-on-Silicon mass production. Specific attention is paid to the three most advanced device structures: lateral transistors, vertical power devices, and nanowire-based HEMTs. Other relevant topics covered by the book are the strategies for normally-off operation, and the problems related to device reliability. The last chapter reviews the switching characteristics of GaN HEMTs based on a systems level approach. This book is a unique reference for people working in the materials, device and power electronics fields; it provides interdisciplinary information on material growth, device fabrication, reliability issues and circuit-level switching investigation.

Efficient power conversion is essential to face the continuously increasing energy consumption of our society. GaN based vertical power field effect transistors provide excellent performance figures for power-conversion switches, due to their capability of handling high voltages and current densities with very low area consumption. This work focuses on a vertical trench gate metal oxide semiconductor field effect transistor (MOSFET) with conceptional advantages in a device fabrication preceded GaN epitaxy and enhancement mode characteristics. The functional layer stack comprises from the bottom an n+/n--drift/p-body/n+-source GaN layer sequence. Special attention is paid to the Mg doping of the p-GaN body layer, which is a complex topic by itself. Hydrogen passivation of magnesium plays an essential role, since only the active (hydrogen-free) Mg concentration determines the threshold voltage of the MOSFET and the blocking capability of the body diode. Fabrication specific challenges of the concept are related to the complex integration, formation of ohmic contacts to the functional layers, the specific implementation and processing scheme of the gate trench module and the lateral edge termination. The maximum electric field, which was achieved in the pn- junction of the body diode of the MOSFET is estimated to be around 2.1 MV/cm. From double-sweep transfer measurements with relatively small hysteresis, steep subthreshold slope and a threshold voltage of 3 - 4 V a reasonably good Al2O3/GaN interface quality is indicated. In the conductive state a channel mobility of around 80 - 100 cm2/Vs is estimated. This value is comparable to device with additional overgrowth of the channel. Further enhancement of the OFF-state and ON-state characteristics is expected for optimization of the device termination and the high-k/GaN interface of the vertical trench gate, respectively. From the obtained results and dependencies key figures of an area efficient and competitive device design with thick drift layer is extrapolated. Finally, an outlook is given and advancement possibilities as well as technological limits are discussed.

This book discusses the important technological aspects of the growth of GaN single crystals by HVPE, MOCVD, ammonothermal and flux methods for the purpose of free-standing GaN wafer production.