(Invited) Selective Area Doping in Gallium Nitride: A Retrospective of the ARPA-E PNDIODES Program

Abstract

A retrospective of the Power Nitride Doping Innovation Offers Devices Enabling SWITCHES (PNDIODES) program launched in 2017 by the Advanced Research Projects Agency-Energy (ARPA-E) of the U.S. Department of Energy will be provided. As silicon-based semiconductors are fast approaching their performance limits for high power requirements, wide-bandgap semiconductors such as gallium nitride and silicon carbide with their superior electrical properties are likely candidates to replace silicon in the near future. The objective of the PNDIODES program was to address the lack of a viable selective area doping processes in gallium nitride (GaN) which is a major barrier to fabricating GaN power electronic devices. At the launch of the PNDIODES program, the selective area doping processes commonly used for other semiconductor materials, such as ion implantation or solid-state diffusion, had not produced satisfactory p-type regions or p-n junctions in GaN. This is due to the thermodynamic decomposition of GaN at high temperatures which limits the available device fabrication processes resulting in poor electrical performance that is insufficient for power electronic applications. The PNDIODES program focused on the mechanistic understanding of the selective area doping process and the development of transformational processes in order to demonstrate arbitrarily placed, reliable, contactable, and generally useable p-n junction regions in GaN. The paper includes a discussion of the origins of the PNDIODES program, the progress and challenges of the selective area doping processes developed under the PNDIODES, and a description of the associated advanced nanoscale characterization techniques developed to investigate the local optical, chemical, structural, and electrical properties of the selectively doped regions. Thoughts on the future trends of GaN device development is offered including innovative device ideas being explored such as superjunction devices, light triggered photoconductive devices, and integrated circuits.