Greener technologies for more efficient power generation, distribution, and delivery in sectors ranging from transportation and generic energy supply to telecommunications are quickly expanding in response to the challenge of climate change. Power electronics is at the center of this fast development. As the efficiency and resiliency requirements for such technologies can no longer be met by silicon, the research, development, and industrial implementation of wide bandgap semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) are progressing at an unprecedented pace. This issue of MRS Bulletin, although certainly not exhaustive, provides an overview of the pace and quality of research revolving around GaN and SiC power electronics, from the choice of substrates, film growth, devices, and circuits to examples of applications.

This article reviews the development of SiC and GaN devices for power-switching applications in the context of four specifically identified application requirements: (1) high-blocking voltage, (2) high-power efficiency, (3) high-switching speed, and (4) normally OFF operation. Specific device and material characteristics, such as ON resistance, parasitic capacitances, and energy-gap values, are compared and discussed in relation to the identified application requirements. Following a review of the fundamental limitations of silicon as a material, this article describes the material advantages that motivated the development of commercially available Schottky diodes and transistors using SiC. The last section analyzes the potential of GaN to enable further technical progress beyond the theoretical limit of Si and to significantly reduce the cost of power-electronic switches.

The methodologies, results, and status of investigations for the development of solvothermal, vapor-phase transport, and solution techniques for bulk crystal growth of large diameter GaN and AlN crystals are presented. This work is being driven by (1) the anticipated need for the initial homoepitaxy of ever-thicker GaN films having very low densities of both threading dislocations and unintentionally introduced, electronically important impurities for devices operating at high and very high load levels; (2) the desire to move from lateral to vertical device structures; and (3) recent results of near theoretical breakdown behavior and near system-level performance in vertical GaN diodes grown on GaN substrates. The choice of the substrate dictates the technique and process routes for the growth of Group III-nitride-based thin films and material device structures. Organometallic vapor-phase epitaxy is the commercial process route of choice for the growth of Group III-nitride films. A review of the precursor gases used in this technique, their stability in the growth reactor and reactivity with nitrogen-containing gases, and the choice of diluent for the growth of films of different nitrides is also presented.

Recent successes with the fabrication of high-performance GaN-based heterostructures on silicon substrates have made this technology very promising. However, epitaxial growth of GaN on Si is challenging. This article presents some of the challenges of epitaxial growth of GaN-on-Si substrates focusing on basic aspects that are pertinent to consider for power electronics.

Transistors with 600 V blocking capability and low switching losses are needed for converting one-phase 230 V mains voltage to lower voltage levels in switch-mode power supplies. The transistors operate as a switch and have to block the system voltage with minimized leakage currents in the OFF-state and have to conduct the current in the ON-state with minimized ON-state resistance. Additionally, any switching losses inside the transistor during the transitions in-between OFF and ON-states need to be minimized for efficient power-converting systems. Efficient high-voltage switching using gallium nitride (GaN)-based power transistors requires excellent material properties in the GaN/AlGaN epitaxial layers in conjunction with optimized process modules and device layout. In the example presented here, GaN buffer compositions and device geometry have been optimized to obtain very low vertical and lateral OFF-state leakage currents at 600 V drain bias and to enable a fast device turn-on with only a minor increase in dynamic ON-state resistance. The developed technology was applied to GaN layers grown on SiC and Si substrates to allow a direct comparison of both static and dynamic device parameters. By implementing a p-type GaN gate, normally OFF operation was realized for 70 mΩ/600 V transistors on both substrates. The new GaN-based devices outperform established Si-based superjunction metal oxide semiconductor field-effect transistors in terms of gate charge and switching energy.

Silicon carbide (SiC) is the next-generation power semiconductor material, enabling an energy-efficient future society by drastically reducing energy loss in existing power electronics systems. SiC metal oxide semiconductor field-effect transistors (MOSFETs) are promising low-loss power-electronics devices. We have developed precisely controlled doping techniques for ultrathin and highly doped SiC epitaxial films and applied this to form the channels of SiC-MOSFETs. This has resulted in the successful formation of diode-integrated MOSFETs (DioMOSs), a structure enabled using SiC semiconductor material. The MOSFET current together with the diode current of the DioMOS is designed to maintain low conduction loss and good temperature stability. The high threshold voltage of MOSFETs and the perfect unipolar conduction with fast switching contribute to safety and low-loss operation. DioMOS offers a single-chip solution for next-generation power electronics compared to the parallel connection using a diode and a transistor in a conventional semiconductor device. DioMOS achieves a small and light direct current converter with high voltage, current, efficiency, and power density applicable to electric and hybrid vehicles.

High-temperature electronic applications are presently limited to a maximum operational temperature of 225°C for commercial integrated circuits (ICs) using silicon. One promise of silicon carbide (SiC) is high-temperature operation, although most commercial efforts have targeted high-voltage discrete devices. Depending on the technology choice, several processing challenges are involved in making ICs using SiC. Bipolar, metal oxide semiconductor field-effect transistors, and junction field-effect transistor technologies have been demonstrated in operating temperatures of up to 600°C. Current technology performance and processing challenges relating to making ICs in SiC are reviewed in this article.

Energy savings and efficient usage of electric power are some of the most urgent issues for future sustainable development of human society. Power electronics is recognized as a key technology in this regard, and the innovation of power electronics is increasingly required. The important role of power electronics innovations in the future human society and a technology roadmap of power electronics utilizing wide bandgap semiconductors, which are typically represented by silicon carbide, are presented. This roadmap consists of several different domains in technology, from the materials side to the applications side. On this roadmap, three generations are defined as technological streams. Based on this roadmap, recent progress in silicon carbide power electronics is reviewed, and future prospects are discussed.

Innovations in materials for next-generation displays and rechargeable batteries are proposed based on the device technology roadmap. With this future perspective, technical concepts and recent achievements at Samsung Electronics for organic semiconductors, inorganic nanomaterials, and optical film materials for display devices as well as energy storage, conversion, and ion transport materials for rechargeable batteries are described. New materials for future devices such as wearable, stretchable, and sensitivity devices are also discussed.