Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

Silicon-based power devices are reaching their fundamental performance limit. The use of wide-bandgap semiconductors with superior material properties over silicon offers the potential for power electronic systems with much higher power densities and higher conversion efficiency. GaN, with a high critical electric field and carrier mobility, is considered one of the most promising candidates for future high-power, high frequency and high temperature applications. High voltage transistors and diodes based on both lateral and vertical structures are of great interest for future power electronics. Particularly, vertical GaN power devices have recently attracted increasing attention due to their many unique properties. This paper reviews recent progress and key remaining challenges towards the development of high-performance vertical GaN transistors and diodes with emphasis on the materials and processing issues related to each device architecture.

This work presents the first experimental study on capacitances, charges and power-switching figure-of-merits (FOMs) for a large-area vertical GaN power transistor. A 1.2 kV, 5 A GaN vertical power FinFET was demonstrated in a chip area of 0.45 mm 2 , with a specific on-resistance of 2.1 mΩ•cm 2 and a threshold voltage of 1.3 V. Device junction capacitances were characterized and their main components were identified. This was used to calculate the switching charges and practical switching frequencies. Device FOMs were then derived that take into account the trade-offs between conduction and switching power losses. Our GaN vertical FinFETs exhibit high frequency (~MHz) switching capabilities and superior switching FOMs when compared to commercial 0.9-1.2 kV Si and SiC power transistors. This work shows the great potential of GaN vertical FinFETs for next-generation medium-voltage power electronics.

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GaN technology is not only gaining traction in power and RF electronics but is also rapidly expanding into other application areas including digital and quantum computing electronics. This paper provides a glimpse of future GaN device technologies and advanced modeling approaches that can push the boundaries of these applications in terms of performance and reliability. While GaN power devices have recently been commercialized in the 15–900 V classes, new GaN devices are greatly desirable to explore both higher-voltage and ultra-low-voltage power applications. Moving into the RF domain, ultra-high frequency GaN devices are being used to implement digitized power amplifier circuits, and further advances using the hardware–software co-design approach can be expected. On the horizon is the GaN CMOS technology, a key missing piece to realize the full-GaN platform with integrated digital, power, and RF electronics technologies. Although currently a challenge, high-performance p-type GaN technology will be crucial to realize high-performance GaN CMOS circuits. Due to its excellent transport characteristics and ability to generate free carriers via polarization doping, GaN is expected to be an important technology for ultra-low temperature and quantum computing electronics. Finally, given the increasing cost of hardware prototyping of new devices and circuits, the use of high-fidelity device models and data-driven modeling approaches for technology-circuit co-design are projected to be the trends of the future. In this regard, physically inspired, mathematically robust, less computationally taxing, and predictive modeling approaches are indispensable. With all these and future efforts, we envision GaN to become the next Si for electronics.

We study the performance of GaN nanowire n-MOSFETs (GaN-NW-nFETs) with channel length, Lg=5 nm based on fully ballistic quantum transport simulations. Our simulation results show high ION=1137 μA/μm and excellent ON-OFF characteristics with Q=gm/SS=188 μS-dec/μm-mV calculated for IOFF=1 nA/μm and VGS=VDS=VCC=0.5 V. These results represent (i) ~15% higher ION than Si-NW-nFET, and (ii) ~17% better Q than Si-NW-nFET, all with Lg=5 nm, thus suggesting the GaN n-channel an intriguing option for application in logic at sub-10 nm channel length. The superior performance of GaN channel compared to Si and other semiconductors at this scaled dimension can be attributed to its relatively higher effective mass of electron and lower permittivity.