Yuji Zhao has made a career out of making electronics more efficient using light-based technology. This work and his exploration into the quantum photonics realm recently put him in the national spotlight.
Zhao, an assistant professor of electrical and computer engineering in the Ira A. Fulton Schools of Engineering at Arizona State University, was awarded the Presidential Early Career Award for Scientists and Engineers in July.
The award is considered the highest honor bestowed by the U.S. government upon outstanding engineers and scientists embarking on careers of promising research and leadership. He joined two additional 2019 PECASE Award recipients from ASU and more than 300 early career faculty from universities across the country who were awarded this honor.
“This is a great honor for myself and my research team,” Zhao said. “We are extremely thrilled to see our work being recognized and we will continue to keep up the good work. It is also a recognition for the world-class research that is being carried out at the School of Electrical, Computer and Energy Engineering and the Fulton Schools at ASU.”
Quantum computing possibilities light up with photonics
The PECASE Award supports Zhao’s project to advance the fundamental sciences in quantum photonics. With $1 million in funding from the U.S. Army Research Office provided through the PECASE Award, Zhao and his research team will advance new scientific understandings to enable the development of a special computing chip called a photonic integrated circuit, or PIC. PICs use photons, or light, to perform complicated tasks rather than electrons, which are used in conventional integrated circuits, or ICs.
“We are developing the world’s first PIC that can produce optical frequency comb at ultraviolet to visible wavelengths,” Zhao said. “They will replace the conventional large and heavy desktop optical setups with tiny semiconductor chips, which will enable us to study new quantum phenomena at a much smaller scale (the nanoscale) with much higher precisions, and enable new applications in quantum computing and biomedical sensing.”
A frequency comb is a tool that uses lasers to emit pulses of light and measures properties of wavelengths of light, which look like the teeth of a comb.
Zhao is working on the five-year project, “On-Chip Frequency Comb Generation at Visible Wavelengths Using III-Nitride Photonic Integrated Circuits” with his doctoral students Hong Chen and Jingan Zhou. Collaborators on the project include ASU electrical and computer engineering Professor Cun-Zheng Ning and researchers from the University of Southern California and the University of California, Los Angeles.
A prolific early career leading gallium nitride research
Zhao is a prominent gallium nitride, or GaN, researcher who has earned approximately $5 million in funding from the Department of Energy Advanced Research Projects Agency-Energy, the Department of Defense, the National Science Foundation and NASA over the past few years for GaN and III-nitride semiconductor-related research. His efforts are laying the foundation for faster, more efficient and higher-powered electronics.
GaN is what is known as a wide-bandgap semiconductor material. Its material properties allow for semiconductor devices to be smaller and operate more efficiently at higher voltages, frequencies and temperatures than silicon-based semiconductor materials.
During his doctoral studies at the University of California, Santa Barbara, Zhao developed GaN light-emitting diodes and lasers with world-record efficiency, “which made significant impacts in the field of solid-state lighting and displays,” he said.
Since he joined ASU in 2014, he and his research group have been developing new GaN devices for power electronics, space missions and quantum photonics applications — progress that has led to more than 70 journal and conference research papers published in the past five years.
In 2016, Zhao was awarded the Fulton Schools’ first NASA Early Career Faculty Space Tech Research Grant, which supported his research to create high-temperature-resistant solar cells.
Zhao’s GaN work has also caught the attention of the U.S. Department of Energy for its applications in making power electronics — switches that convert electricity from one form to another to be used by chargers and electrical grids — more powerful, efficient and compact. For a $1.5 million project funded by the DOE Advanced Research Projects Agency-Energy’s PNDIODES program, Zhao was selected to address technological gaps in GaN doping, or adding impurities, a critical technical step to achieving high-performance GaN power devices.
His GaN and solar cell work also has been recognized for its benefits in applications out of this world. Zhao attended the 2017 NASA Tech Day as one of only three university faculty members invited to join NASA’s senior leadership to talk about space technology with U.S. Congress members in Washington, D.C. He explained how his GaN work enables solar technology to retain its performance in high temperatures, something that isn’t possible with silicon-based solar cells. This technology is especially useful for missions to the extremely hot planet Mercury.
Zhao also received the Science Foundation Arizona Bisgrove Scholar Award to support his proposal to develop “smart” LEDs that can heal wounds and even replace current Wi-Fi technology with “Li-Fi,” or light-based wireless communications with 10,000 times the bandwidth capacity.
That work, which was at the time a relatively untested area of photonics and LED research, has yielded 20 papers published in leading research journals and in the publications of international conferences.
The U.S. Department of Defense has also supported Zhao's work to counter weapons of mass destruction by using aluminum nitride to create transistors capable of withstanding high voltage and radiation damage.
Supporting the next generation of gallium nitride researchers
Zhao is also proud of the outstanding students and young researchers who have emerged from his research group. Those include graduate students who have been recognized for contributions to advances in GaN research. In spring 2019, Zhao’s first doctoral student, Houqiang Fu, earned the Fulton Schools’ 2019 Palais Outstanding Doctoral Student Award, ASU’s highest honor for recognizing exceptional electrical engineering doctoral students excelling in research and academics.
His second doctoral student, Zhijian Lu, went on to a successful academic career as an assistant professor at the Southern University of Science and Technology, China. Zhao’s visiting scholar, Xiaodong Zhang, is now an associate professor at the Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Science.
“At ASU, there is nothing that makes us more proud than to see our students being successful,” Zhao said.
After only five years into his own successful academic career, Zhao has already made great strides in his area of expertise. The PECASE Award demonstrates he is looking at a bright future as a research leader.
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