PhD Defense: "Design and Epitaxial Growth of Ultra-scaled N-polar GaN/(In, Al, Ga) NHEMTs by Metal Organic Chemical Deposition and Device Characterization"

Jing Lu

December 16th (Monday), 12:00pm
Engineering Science Building (ESB), Room 2001

N-polar GaN HEMTs have shown to be attractive for high-frequency applications with the following advantages over Ga-polar HEMTs: (a) the existence of a natural back barrier increases electron confinement, and (b) very low contact resistances to the 2DEG. To achieve high current-gain (fT) and maximum oscillation frequencies (fmax), the gate length has been aggressively scaled below 100-nm. Meanwhile, scaling down the channel-thickness (tch) is essential for the mitigation of short-channel effects. However, this vertical scaling can degrade charge density (ns) and mobility (μ), largely reducing channel-conductivity. In this work, the vertical Epi scaling of N-polar GaN/(Al, In, GaN)N HEMTs was investigated. The epitaxial design space and MOCVD growth techniques for achieving high conductivity for ultra-thin channel GaN/(Al, In, GaN)N HEMTs were explored. By engineering the charge inducing back barrier, the channel thickness was successfully scaled down to 3-nm with a low sheet resistance of 329 Ω/□. Devices with 5-nm-thick channels exhibited sheet resistance of 230 Ω/□, peak gm of 1887 mS/mm, fT of 201GHz, and fmax of 406GHz. Additionally, the implementation of a gating cap layer for the N-polar HEMTs was investigated to reduce gate leakage and improve breakdown voltage. By inserting a thin InAlN cap layer on top of the GaN channel layer, devices with 500 V breakdown and 3.4W/mm RF power were demonstrated.

About Jing Lu:

photo of jing luJing Lu 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.S. and M.S in Electrical Engineering from Tsinghua University, China in 2008 and joined the Mishra group in 2009. As part of her graduate research work, she has worked on MOCVD growth of GaN-based electronic devices, mainly on N-polar GaN HEMTs.

Hosted by: Professor Umesh Mishra