Recent years have witnessed a tremendous development of vertical gallium nitride (GaN) power devices, a new class of device technology that could be the key enabler for next-generation high performance power electronics. In this comprehensive review, we discuss the recent progress made on vertical GaN power devices, highlighting their important device design principles and fabrication processes. Part I of the two-part review series introduces the basic design principles of vertical GaN devices using Schottky barrier diodes (SBDs) and p-n diodes as examples. We provide a comprehensive review and in-depth analysis on their basic structures, fabrication processes, and device physics. Materials engineering, including buffer layer and drift layer design, and device engineering, including various edge termination methods, are elucidated. Key device topics, including avalanche breakdown and leakage mechanisms of vertical GaN power devices, are also discussed. We also examine various approaches and provide detailed descriptions of the key knowledge obtained. This timely review provides valuable information for the power electronics community and can inspire researchers for future interdisciplinary collaborations in this emerging and exciting research field.

Vertical gallium nitride (GaN) power devices are enabling next-generation power electronic devices and systems with higher energy efficiency, higher power density, faster switching, and smaller form factor. In Part I of this review, we have reviewed the basic design principles and physics of building blocks of vertical GaN power devices, i.e., Schottky barrier diodes and p-n diodes. Key topics such as materials engineering, device engineering, avalanche breakdown, and leakage mechanisms are discussed. In Part II of this review, several more advanced power rectifiers are discussed, including junction barrier Schottky (JBS) rectifiers, merged p-n/Schottky (MPS) rectifiers, and trench metal-insulator-semiconductor barrier Schottky (TMBS) rectifiers. Normally- OFF GaN power transistors have been realized in various advanced device structures, including current aperture vertical electron transistors (CAVETs), junction field-effect transistors (JFETs), metal-oxide-semiconductor field-effect transistors (MOSFETs), and fin field-effect transistors (FinFETs). A detailed analysis on their performance metrics is provided, with special emphasis on the impacts of key fabrication processes such as etching, ion implantation, and surface treatment. Lastly, exciting progress has been made on selective area doping and regrowth, a critical process for the fabrication of vertical GaN power devices. Various materials characterization techniques and surface treatments have proven to be beneficial in aiding this rapid development. This timely and comprehensive review summarizes the current progress, understanding, and challenges in vertical GaN power devices, which can serve as not only a gateway for those interested in the field but also a critical reference for researchers in the wide bandgap semiconductor and power electronics community.

Wide and ultrawide-bandgap (U/WBG) materials have garnered significant attention within the semiconductor device community due to their potential to enhance device performance through their substantial bandgap properties. These exceptional material characteristics can enable more robust and efficient devices, particularly in scenarios involving high power, high frequency, and extreme environmental conditions. Despite the promising outlook, the physics of UWBG materials remains inadequately understood, leading to a notable gap between theoretical predictions and experimental device behavior. To address this knowledge gap and pinpoint areas where further research can have the most significant impact, this review provides an overview of the progress and limitations in U/WBG materials. The review commences by discussing Gallium Nitride, a more mature WBG material that serves as a foundation for establishing fundamental concepts and addressing associated challenges. Subsequently, the focus shifts to the examination of various UWBG materials, including AlGaN/AlN, Diamond, and Ga₂O₃. For each of these materials, the review delves into their unique properties, growth methods, and current state-of-the-art devices, with a primary emphasis on their applications in power and radio-frequency electronics.

This manuscript provides an overview of power semiconductor devices (PSDs) for distributed energy resource (DER) system. To begin with an overview on electrically-triggered SiC and GaN devices followed by a brief narration of ultra-wide-bandgap (UWBG) PSDs. Subsequently, an overview of optically-activated PSDs encompassing photoconductive semiconductor switch (PCSS) and optical bipolar PSDs are provided. Finally, an overview of PSD packaging and reliability is captured.

Vertical MOSFET is a critical milestone in the gallium oxide (Ga ₂ O ₃ ) roadmap. However, the lack of an effective current blocking layer in Ga ₂ O ₃ , which is essential for any DMOS-like (double-diffused MOSFET) transistors has proved to be the main barrier to the achievement of a vertical MOSFET. Here, we report two novel findings -first, a selective diffusion doping technique utilizing magnesium (Mg) doping spin-on-glass (SOG) as a dopant source to form a current blocking layer (CBL), and second, the first demonstration of a vertical Ga ₂ O ₃ MOSFET with the Mg diffused CBL- Vertical Diffused Barrier Field-Effect-Transistor (VDBFET). The device exhibits an excellent field-effect-transistor (FET) behavior with a high on-off ratio of 10 ⁹ and a decent saturation. Due to the unique nature of the Mg-doped region, the transistor is normally-off with a turn-on voltage of ~7 V. An on-current of 0.15 kA/cm ² is measured with a gate voltage ( ${V}_{g}$ ) of 12 V, and a drain voltage ( ${V}_{d}$ ) of 15 V. The three terminal breakdown voltage measured at a ${V}_{g}$ of 0V is 72 V. The successful demonstration of the first Ga ₂ O ₃ VDBFET significantly brightens the prospect for its application in high power electronics.

Fundamental research and development of ultra-wide bandgap (UWBG) semiconductor devices are under way to realize next-generation power conversion and wireless communication systems. Devices based on aluminum gallium nitride (Al_xGa_1−xN, x is the Al composition), β-phase gallium oxide (β-Ga₂O₃), and diamond give promise to the development of power switching devices and radio frequency power amplifiers with higher performance and efficiency than commercial wide bandgap semiconductor devices based on gallium nitride (GaN) and silicon carbide (SiC). However, one of the most critical challenges for the successful deployment of UWBG device technologies is to overcome adverse thermal effects that impact the device performance and reliability. Overheating of UWBG devices originates from the projected high power density operation and poor intrinsic thermal properties of Al_xGa_1−xN and β-Ga₂O₃. This Perspective delineates the need and process for the “electro-thermal co-design” of laterally configured UWBG electronic devices and provides a comprehensive review of current state-of-the-art thermal characterization methods, device thermal modeling practices, and both device- and package-level thermal management solutions.