Advances in Polarization Engineering and Field Control in III-N Devices

Abstract

Wide bandgap III-N semiconductors are promising for electronic devices operating at high power levels and in harsh environments due to the combination of their excellent carrier transport properties and the ability to operate at high internal electric fields.  However, the performance of many current-generation devices is below the fundamental performance limits expected from the material properties.  This can be addressed through novel device design concepts.  In this talk, recent work on polarization-graded structures for performance enhancement in mm-wave HEMTs, cost-effective edge termination strategies for vertical power devices, and devices exploiting impact ionization and avalanche in GaN will be reviewed.  For example, the use of polarization-grading has been shown to decrease the peak electric field in the channel, increase the breakdown voltage, and improve the power scaling of III-N based HEMTs, without the use of field plates that limit high-frequency performance; experimentally-validated power-added efficiency of 50% at 94 GHz has been achieved.  In vertical devices, device high-field operation is often limited by edge effects; we report a strategy for edge termination that provides a large process window that is tolerant of both fabrication processing and epitaxial layer thickness and doping variations, and enables robust avalanche operation to be achieved in practice.  In addition to increased breakdown voltage, the ability to harness impact ionization and avalanche for device functionality is also critical for avalanche photodiodes and negative-resistance oscillators such as IMPATT diodes. We report the recent demonstration of experimentally-measured negative resistance at microwave frequencies from GaN-based IMPATT diodes, illustrating direct exploitation of the high-field operation of GaN pn junctions for advanced functionality. 

Bio

Patrick Fay is a Professor in the Dept. of Electrical Engineering at the University of Notre Dame; he received a Ph.D. in electrical engineering from the University of Illinois at Urbana-Champaign in 1996.  His research focuses on the design, fabrication, and characterization of microwave and millimeter-wave electronic devices and circuits, power device design and fabrication, as well as the use of micromachining techniques for the fabrication of RF through sub-millimeter-wave packaging.  He established the High Speed Circuits and Devices Laboratory at Notre Dame, as well as oversaw the design, construction, and commissioning of the 9000 sq. ft. class 100 cleanroom housed in Stinson-Remick Hall at Notre Dame, where he has served as the director of this facility since 2003.  Prof. Fay is a fellow of the IEEE, is an IEEE Electron Devices Society Distinguished Lecturer, and has published 11 book chapters and more than 400 articles in scientific journals and conference proceedings.