You build yourself into what you do

Two students whose research aims to improve lighting technologies and reduce energy consumption have won a top international prize.

Guangyu Liu and Jing Zhang, Ph.D. candidates in electrical engineering at Lehigh, will receive the 2012 Scholarship in Optics and Photonics from SPIE, the International Society for Optics and Photonics.

Together with 138 other students from around the world, they will accept their awards next February in San Francisco at Photonics West 2013, SPIE’s annual conference.

Liu and Zhang both earned bachelor’s degrees from Huazhong University of Science and Technology (HUST) in Wuhan, China. Since enrolling at Lehigh, each has published more than 40 articles in journals and conference proceedings.

The two students are advised by Nelson Tansu, the Class of 1961 Associate Professor of Electrical and Computer Engineering.

Toward more efficient LEDs

Their research focuses on improving the light-generating efficiency of solid-state LEDs (light-emitting diodes), which use much less energy than incandescent lighting and promise to exceed the efficiency of fluorescent lighting as well when scientists overcome several challenges.

In additional to theoretical and computational work, the students use the state-of-the-art facilities in Lehigh’s Center for Photonics and Nanoelectronics to design, grow, characterize, fabricate and test devices.

Each has several research projects. Zhang works to identify important structures based on wide bandgap semiconductor alloys to address the difficulty in achieving high optical gain (light amplification) for deep (low-wavelength) ultraviolet lasers. She also seeks to boost the efficiency and device performance in visible-light LEDs by using new substrate and nanophotonics structures.

Zhang also studies the use of nanostructures based on III-Nitride semiconductors for developing thermoelectric materials that enable the active removal of heat from high-power devices such as lasers, transistors and solar cells.

Liu studies current leakage caused by “efficiency droop” in LEDs. The light-generating efficiency of LEDs peaks at low current but begins to diminish significantly at the high current at which low-cost LEDs operate. (Low-cost LEDs require the devices to operate at high current level.) Liu works with with other Ph.D. students in Tansu’s group to solve “efficiency droop” by using new types of barrier designs in LEDs.

Liu is also developing new types of quantum wells to improve the efficiency of green LED diodes. She fabricates quantum-dot structures on a new material that shows potential for ultra-high, uniform dot densities.

Maintaining a steady focus

The students credit their success to the strong foundation in fundamental physics they received at HUST and Lehigh, and to Tansu.

“Our group has been fortunate to have the opportunity to mentor some very talented graduate students,” says Tansu. “These students are very dedicated, focused and enthusiastic.”

“Prof. Tansu is a hands-on adviser,” says Zhang. “He’s always available to answer questions. Also, he tells us stories of other successful individuals in our research fields. These help us keep our energy high.”

Motivation also comes from within, says Liu.

“Getting a Ph.D. takes four or five years. You have to stay focused. In our first year, we try to publish articles and give conference talks very quickly. These help us stay motivated.”

The students take inspiration from Hongping Zhao, two-time SPIE scholarship winner who earned her Ph.D. in 2011 working with Tansu and went directly to Case Western Reserve University as an assistant professor of electrical engineering.

Liu and Zhang hope to follow Zhao’s example. They average 10-12 hours a day working and studying, and they spend much of their free time reading the literature of their field and the biographies of physicists.

“Your mind should be focused at all times on your job,” says Liu. “You think about your projects wherever you go. You build yourself into what you do.”