Jing Zhang, a faculty member at Rochester Institute of Technology, has received a CAREER award from the US National Science Foundation (NSF) for work to develop new, highly efficient ultraviolet light sources.
Zhang’s NSF award of $500,145 is for five years for “Development of high-efficiency ultraviolet optoelectronics: physics and novel device concepts”. The project’s goal is to realize high-efficiency UV photonic devices. The Faculty Early Career Development (CAREER) Program is one of the NSF’s most prestigious awards in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization.
Devices that Zhang’s research group are creating have the potential to demonstrate that a deeper, fairly unrealized range of the ultraviolet (UV) light spectrum is as efficient as existing near-UV used in today’s LED lights. Increasing the efficiencies of optoelectronic devices, specifically using ultraviolet LED technologies, could advance important applications in photolithography, 3D printing, purification systems and sensing applications.
The further along the UV range, the less efficient the technology being produced; however, preliminary physics analysis and tests on device prototypes show promise, Zhang explains.
“What I propose to do is on semiconductor-based UV optoelectronic devices, which are efficient, compact and the lifetime of the devices is very long compared to mercury-based, UV light sources,” says Zhang, an assistant professor in the electrical and microelectronic engineering department in RIT’s Kate Gleason College of Engineering. “Semiconductor materials are environmentally friendly compared to mercury-based UV bulbs. That is why this new type of device we are developing is very promising—if we can deliver higher efficiencies toward those devices.”
The UV light spectrum is being explored further because differing aspects react well with certain bio and chemical agents, which are beneficial for biomedical applications. UV light has also been used for air and water purification systems and to cure resins for 3D printers. Advancing these technologies is becoming more important, but the efficiencies of the UV LEDs are low compared to existing visible LEDs, a mature technology that has been commercially available for more than two decades.
“Shorter wavelengths with the UV devices have efficiencies less than 10%, sometimes even as low as 1%,” notes Zhang. “This is the reason why we really don’t have reliable, commercially available UV LEDs based on semiconductors yet,” she says, adding that the material used for existing LED chips is indium gallium nitride — a narrower-bandgap material. In this new project, Zhang will explore use of the much wider-bandgap material aluminum gallium nitride.
However, AlGaN is less developed because the material is more difficult to grow and often has more defects and dislocations. Zhang has been able to make inroads in this area.
RIT has capabilities in its Semiconductor Manufacturing and Fabrication Laboratory (SMFL), located in the engineering college. In 2016, Zhang also attained an NSF grant to acquire an inductively coupled plasma reactive ion etching (ICP-RIE) system. Researchers can therefore fabricate prototype devices in-house at RIT.
“We have already developed the fabrication process for the UV LEDs; it is already mature in our group,” says Zhang, whose research expertise is in III-nitride semiconductors for photonics and energy applications. “We have developed the physics, and we have promising preliminary results on very initial UV LEDs,” she adds. “We are going to continue the research with these results and see how we can achieve optimized novel device structures.”
