ECE fac candidate, Tomas Palacios

Tomas Palacios is a Ph.D. candidate in ECE at the University of California – Santa Barbara.
NITRIDE-BASED TRANSISTORS THE POWER OF POLARIZATION

In only 15 years, nitride based semiconductors have evolved tremendously from the first material with very high dislocation densities to commercial applications. Nitride semiconductors have a unique set of properties that makes them the most complete semiconductor family. Nitrides have found multiple applications such as LEDs and laser emitters covering from ultraviolet to infrared, surface acoustic wave filters, photodetectors, advanced physical and bio- sensors, transistors, etc.
One of the most characteristic properties of nitride semiconductors is their very high spontaneous and piezoelectric polarization. This polarization is several orders of magnitude higher than in other semiconductors and it induces very high electric fields in the device. The engineering of these electric fields constitutes a new powerful tool to shape the band diagram to improve the performance of electron devices.
In this talk we will present three different examples of the use of polarization engineering to improve the performance of AlGaN/GaN high electron mobility transistors (HEMTs). First, we will introduce the use of an ultrathin AlN layer between the GaN buffer and the AlGaN barrier of a HEMT to improve the electron mobility. The second example will be the GaN-spacer HEMT. In this new transistor, a 1 nm thick AlN layer between two GaN epilayers is enough to induced 2-dimensional electron confinement. The third example of the use of polarization to engineer the band diagram will be the use of an ultrathin InGaN layer below the channel.
Finally, I will conclude my talk with some comments on the use of nitride-based transistors in ultra scaled electronics, where the large band gap of nitride semiconductors, high electron velocity, and the new tools given by polarization engineering will be extremely useful.