Nitrides Seminar - Zachary Biegler
Nitrides Seminar
Thursday, May 29, 2025, 12:00PM
Attend in person at ESB 1001!
Zoom option also available
Zachary Biegler
Graduate Student Researcher, Speck Group
University of California, Santa Barbara
GaN Based Superjunction Diodes for High Power Applications
Power electronics, as a field, requires materials that can efficiently transfer power from one form into another. This often necessitates large voltages and low current in reverse bias blocking, but low turn on voltages and high current in forward bias. In conventional devices, this results in a trade off related to the doping of the drift layer. However, superjunction devices mitigate this trade off through the use of 2D field engineering at the cost of stringent doping control for charge balance. These devices have been shown in Si, as it can somewhat easily create charge balanced structures through ion-implantation and annealing. However, moving to wider bandgap devices (such as GaN, SiC, or β-Ga2O3) can result in a dramatic decrease in the specific-on-resistance for a given breakdown voltage. GaN with its wide bandgap of 3.4 eV and ability to dope both p- and n-type is a promising material system to examine high voltage superjunction devices. Despite these promises, very little experimental work on purely GaN based superjunction devices exists.
In this seminar, we discuss some of the challenges with creating superjunction diodes (both lateral and vertical), some early lateral single channel Schottky superjunction structures, methods of post growth charge balancing, and processes to mitigate unintentionally incorporated ambient impurities (Si, O, C, and H) at regrowth interfaces using a combination of in situ Ga adsorption and desorption cycles and XeF2 exposure for vertical structures. The Schottky superjunction devices show an 86× improvement to reverse bias breakdown, as compared to reference n-GaN Schottky structures, with no degradation to forward on characteristics. Separate intentionally ambient exposed interfaces show ~90% removal of unintentionally incorporated Si with the use of XeF2 in situ surface cleaning. By incorporating the lessons learned from early lateral superjunction devices and the ability to mitigate interfacial ambient impurities, it is possible to move toward fully vertical etch and regrown GaN superjunction diodes.