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Nearly $3 million in DOE awards will advance energy research projects

Professor carefully holds a small wafer with tweezers while in her lab.Professor Hongping Zhao holds a wafer of gallium nitride grown on native substrate in her laboratory.

Ohio State engineering researchers are shining light on gallium nitride as a semiconductor with more potential to improve electricity efficiency and effectiveness. They recently received two separate awards from the U.S. Department of Energy (DOE).

A three-year, $2.2 million project is one of 12 awarded a total of $35 million in federal funding through DOE’s Advanced Projects Agency-Energy (ARPA-E) OPEN+ program. The program aims to discover new ways of harnessing medium-voltage electricity for applications in industry, transportation, on the grid and more, which could greatly improve efficiency and reliability across most of the U.S. economy.

“America’s energy landscape is constantly evolving, and as new ways to generate and distribute power gain popularity, it’s critical we develop the tools to maximize their utility,” said U.S. Secretary of Energy Rick Perry. “These ARPA‑E projects serve first and foremost to modernize how we move power around safely, reliably and efficiently, creating a new set of capabilities for tomorrow’s utilities and industry. ”

Buckeye engineers will develop gallium nitride (GaN) semiconductor materials suitable for high-voltage (15 to 20 kilovolt) power control and conversion. These materials hold the promise of being more efficient as well as smaller and lighter than current devices.

“Currently the market uses mainly silicon for power semiconductors, which becomes much less efficient as power demands increase. Semiconductors based on GaN show great promise to meet the requirements for high-power, high-temperature and high-frequency applications,” said principal investigator Hongping Zhao, associate professor of electrical and computer engineering, and materials science and engineering.

It’s estimated that as much as 80% of electricity could pass through power electronics between generation and consumption by 2030. Advances in power electronics promise enormous energy efficiency gains throughout the U.S. economy, Zhao explained. The Ohio State engineers’ project is ambitious—the highest reported breakdown voltage achieved for this material system so far is around five kilovolts. 

“Currently gallium nitride power electronic devices are mainly targeted for a relatively lower voltage—below one kilovolt,” she said. “Fifteen to 20 kilovolts hasn’t been demonstrated yet, we are really pushing it to the limit.”

Collaborating on the project with Zhao are fellow Ohio State electrical and computer engineering faculty, Professor Siddharth Rajan, Professor Jin Wang and Neal A. Smith Chair Professor of Electrical Engineering Steven Ringel.

Zhao’s research group will synthesize the gallium nitride via a unique version of the industry-adopted chemical reaction process known as metal-organic chemical vapor deposition. Using their novel method, Zhao hopes to accelerate the material growth rate so that the targeted thickness can be achieved in much less time.

Two researchers work on equipment that synthesizes semiconductor materials, one at the computer and another with the GaN material.PhD student Yuxuan Zhang (left) and postdoctoral researcher Zhaoying Chen are part of the research team focused on synthesizing gallium nitride.Rajan’s team is focusing on device design, optimization and fabrication in order to create longer lasting devices capable of withstanding much higher voltages. Meanwhile, Ringel’s group is studying defects in the gallium nitride material and how those will affect device performance, especially at high-voltage operation, and Wang’s group will develop novel packaging and perform reliability testing.

Having the diverse expertise needed for this project at one university, let alone the same department, is unique, Zhao noted.

“Not many places have this comprehensive capability,” she said. “We cover a wide spectrum from fundamental material synthesis to defect characterization, device fabrication, packaging and circuit testing. This is a very unique vertical integration.”

Shining new light on LED efficiency

Zhao also recently received nearly $600,000 from the DOE to create high-efficiency, indium gallium nitride-based LEDs in green, amber and longer wavelengths.

The funding is part of $42 million recently awarded by the DOE to support early-stage research and development of innovative residential and commercial building technologies to help consumers and businesses save energy costs and drive domestic economic competitiveness.

While solid-state lighting technology like LEDs seem quite mature, there is still room for advances, explained Zhao, who began working on solid-state lighting research as a doctoral student.

“There are still key challenges that need to be addressed. One of the key challenges for LEDs for solid-state lighting is low efficiency at green, amber and yellow,” she said. “In this project, we will develop novel materials and structures to address this issue."

Commercially available white LEDs are actually high-efficiency blue LEDs mixed with yellow phosphors to emit white light. By increasing the efficiency of green, amber and yellow LEDs, researchers can potentially fabricate true white LEDs, which they expect to be much more efficient.

“This is actually a big deal,” Zhao explained. “Because phosphors cause a lot of issues—lower efficiency, lifetime degradation, especially at high temperatures and high-humidity conditions.”

Zhao’s team proposes a unique strategy to achieve this feat, using a customized metal-organic chemical vapor deposition system that will enable them to develop a new type of nitride semiconductor based on the group II-IV-nitride material system.

“Theoretical prediction indicates that it can significantly improve the efficiency of LEDs emitting in the green, amber and yellow. We are very optimistic about the great promise for this technology.”

The project is a collaboration with co-investigator Kathleen Kash, professor and chair of physics at Case Western Reserve University.

by Candi Clevenger, College of Engineering Communications, clevenger.87@osu.edu