Research Experiences for Undergraduates

Gallium nitride (GaN) has become established as an important semiconductor in photonics due to its success in blue light-emitting diodes and lasers; but its applications to digital and power electronics so far are very limited because of the lack of a silicon metal oxide semiconductor (MOS)-like process for building integrated circuits.  To overcome this limitation, researchers at the Center for Power Electronics Systems (CPES), an Engineering Research Center based at Virginia Polytechnic Institute and State University, in 2006 demonstrated the world’s best ion-implanted, enhancement mode, n-channel GaN Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) on p and n GaN epi on sapphire substrates that already delivers 30% better performance than traditional MOSFETs.

This progress in n-channel MOSFET is a major step toward the ultimate demonstration of a high-voltage MOS-gated bi-directional switch in GaN.  But before such a demonstration could be made, what was needed was a complementary pair of reverse blocking MOSFETs connected in parallel. In 2007, CPES researchers achieved this signficant milestone by successfully demonstrating the world’s first high-voltage, monolithically integrated GaN MOSFET/Schottky rectifier pair that functions in parallel.  (A rectifier is an elec trical device that converts alternating current to direct current).  This integrated device, with its schematic cross-section shown in Fig. 1 and a microphotograph of one of the test devices shown in Fig. 2, has forward and reverse blocking and conduction capabilities. The CPES investigators have characterized functional devices with forward and reverse blocking voltages as high as 770V and 1050V, respectively. This integrated GaN MOSFET/rectifier is a new, generic device building-block, with fewer components or packaging problems–allowing power electronics systems to deliver power more efficiently.

GaN power devices are expected to be much more efficient than their silicon counterparts, thus reducing energy consumption and eliminating or at least reducing the cooling accessories needed in power electronics systems. In addition, and very importantly, the GaN MOS process that CPES has developed is compatible with and usable in state-of-the-art silicon chip foundries in terms of temperature, thin film deposition, and process equipment-unlike the silicon carbide MOS processes, which are not compatible and require higher temperatures.

Primary Strategic Outcome Goal:
Engineering Research Centers

Secondary Strategic Outcome Goals:
Other Infrastructure and Research Resources

How does this highlight address the strategic outcome goal(s) as described in the NSF Strategic Plan 2006-2011 ?
GaN power devices using GaN MOSFETs integrated with rectifiers, as developed and demonstrated here, will be much more energy efficient than their silicon counterparts, and easier to manufacture in high volume in existing chip foundries. The research underlying this advance is highly innovative, cross-disciplinary, and requires a complex systems approach.


Does this highlight represent transformative or potentially transformative research?  If so, please explain why. For more information, see  Report to Congress: Transformative Research at the National Science Foundation, April 16, 2008
No


Does this highlight represent Broadening Participation?  If so, please explain why.
For more information, see  Broadening Participation at the National Science Foundation: A Framework for Action
No


Are there existing or potential societal benefits of this research? It is important for NSF to be able to provide examples of NSF-supported research that have societal benefits, including benefits to the U.S. economy.
For more information, see  Excerpt from Merit Review Broader Impacts Criterion:
Representative Activities, July 2007
Yes
The ability to use a silicon MOS-like process for building integrated circuits in gallium nitride will enable a new generation of digital and power electronics devices for use in computer and other technologies that reduces energy consumption with reduced need for cooling.

ENG/EEC 2008