PhD Defense: "Gallium Nitride Vertical Electron Transistors for High Power Applications"

Ramya Yeluri

November 22nd (Friday), 10:30am
Bren Hall, Room 1414

Lateral GaN HEMT structures have been well studied and developed for high power applications. However, for very high breakdown voltages, a vertical device design is more favorable owing to the better field distribution and higher power density. Current Aperture Vertical Electron Transistors (CAVETs) benefit from the high electron mobility of the 2-dimensional electron gas (2-DEG) in the lateral direction and better field distribution in the vertical direction. Current flows laterally in the 2-DEG at the AlGaN/GaN heterojunction and is directed vertically down to the drain through an aperture. A current blocking layer (CBL) is used to define the low resistance aperture. The focus of this thesis is developing CAVETS with Mg-doped conductive p-GaN layers as the current blocking layer. Current blocking is realized by the use of a reverse biased p-n junction as opposed to an insulating layer.

The p-GaN is regrown either by Ammonia MBE or MOCVD and in order to ensure that the p-GaN layer remains active, the channel regrowth is done by Ammonia-MBE. The current blocking capacity of the p-n junction has been verified in an n/p/n structure and the highest breakdown voltage recorded was 870 V. Peak electric field has been estimated to be 3.1 MV/cm, which is close to the GaN critical field. With the current blocking capacity of the active p GaN layer verified, selective area regrowth was used to define the apertures and CAVETs were fabricated. Promising transistor performance was demonstrated with a high saturation current of 10.9 kA/cm2 and very low ON-resistance of 0.4 mΩ cm2.

About Ramya Yeluri:

photo of ramya yeluriRamya Yeluri is a Ph.D. candidate in the Electrical and Computer Engineering Department at University of California, Santa Barbara and is guided by Professor Umesh K. Mishra. She received her B.Tech. in Engineering Physics in 2007 from the Indian Institute of Technology Madras and M.S. in Electrical and Computer Engineering in 2009 from the University of California, Santa Barbara. As part of her graduate research work, she has worked on GaN vertical electron transistors as well as dielectric/GaN interface characterization.

Hosted by: Professor Umesh K Mishra