After decades of research, the wide-bandgap (WBG) semiconductors GaN and SiC are beginning to enjoy commercial success for power electronics applications. Both high breakdown voltage and low on-state resistance are important factors that have enabled improved performance and efficiency of power switching transistors based on these WBG semiconductors. However, truly dramatic improvements in power device performance for extreme applications are likely to require a new class of semiconductor materials with bandgaps greater than that of GaN (3.4 eV), the so-called “ultra” wide-bandgap (UWBG) semiconductors. The critical electric field (E_C) affecting breakdown scales approximately as E_g^2.5 [1], making the UWBG semiconductors capable of extremely high voltage operation. In particular, Al-rich AlGaN alloys approaching AlN with its 6.2 eV bandgap have an estimated E_C that may be nearly 5x that of GaN, and nearly 2x that of ß-Ga₂O₃, another UWBG material that is currently receiving increased research interest.

Since the first report of an AlGaN-channel transistor [2], progress has been steady and an increasing number of approaches to realizing Al-rich devices have been evaluated. High electron mobility transistors have been realized at channel concentrations as high as 85% Al [3]. However, research into this material for power applications is in its early days, and many challenges remain to be addressed in epitaxial growth, defect physics, fundamental material properties, device processing, and how these relate to device design.

This talk will describe Sandia National Laboratories’ efforts to develop Al-rich AlGaN into the material of choice for next-generation power electronics applications. Research will be motivated by comparing power switching figures of merit against ß-Ga₂O₃ and other UWBG semiconductors being considered for future power electronics applications. The latest results in AlGaN-channel HEMTs will be described, including improvements in current density, recent approaches to realizing enhancement-mode operation, and analysis of the device characteristics over a range of temperature and bias conditions. Details regarding ongoing work to optimize device performance for Al-rich AlGaN transistors will be presented in the talk and final proceedings paper.

This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.

[1] R. J. Kaplar, et al., ECS J. Solid State Science and Technology, vol. 6, p. Q3061 (2017).

[2] T. Nanjo, et al., Appl. Phys. Lett. 92, 263502 (2008).

[3] A.G. Baca, et al., Appl. Phys. Lett. 109, 033509 (2016).