Arthur Xiao wins SID Detroit Metro Chapter Academic Award for work on red micro-LEDs

Mena Davidson • October 3, 2024

Xiao’s PhD work has focused on developing tiny, efficient, and stable red LEDs for use in virtual and augmented reality displays.

Yixin “Arthur” Xiao, PhD student in Electrical and Computer Engineering (ECE) is a 2024 recipient of the Society for Information Displays (SID) Detroit Metro Chapter Academic Award, which recognizes graduate students working on advanced display technology.

For the past five years, Xiao has been working with advisor Prof. Zetian Mi to develop the world’s smallest red-emitting III-nitride LEDs, suitable for virtual and augmented reality (VR/AR) applications. III-nitride LEDs smaller than a micrometer, known as micro-LEDs, enhance the resolution of electronic displays––often at the expense of efficiency, due to damage incurred during the fabrication process.

Previous work in Mi’s research group increased the stability of red micro-LEDs by adding indium gallium nitride (InGaN) to the devices, but the high concentration of indium can lead to material instability. Therefore, red micro-LEDs remain more difficult to produce and demonstrate than blue and green micro-LEDs.

“The comparative lag in the development of red-emitting III-nitride micro-LEDs is a bottleneck to the realization of next-generation RGB displays,” said Xiao.

Xiao has continued this work, using an innovative new method to stabilize the material and further increase efficiency of red micro-LEDs for practical use. Using bottom-up selective area epitaxy, Xiao fabricates micro-LED devices without exposing them to damaging plasma. This method also allows him to manage the stress on the material, stabilizing it even in the presence of the indium.

“Material stress management is crucial for achieving the levels of efficiency and indium incorporation thus far out of reach for conventional top-down III-nitride micro-LEDs,” said Xiao. “This development is a game changer: it enables the achievement of high efficiency (sub)micrometer scale LEDs that were not previously possible.”

Xiao, Mi, and colleagues were able to demonstrate a green micro-LED more efficient than the OLEDs used for cell phone screens, as well as a red micro-LED an order of magnitude more efficient than existing red LEDs of a similar size.

However, the team didn’t stop there––having engineered a more efficient red micro-LED, Xiao focused on the color quality. At high electric currents, InGaN red micro-LEDs tend to show blueshifting, meaning that the wavelength of light shifts toward a higher-frequency, blue color.

“Such a shift in color at different device power levels seriously hinders the device dynamic range and the display experience, if increasing the brightness of the device turns the red pixels into orange or yellow ones,” Xiao explained.

A horizontal bar with shifting rainbow colors from left to right is labeled "blueshift" with arrows showing a shift toward the right, purple side of the spectrum. Below that, a string of lights shifts from red to yellow. Below that, an identical rainbow bar is labeled "redshift", with arrows pointing to the right, toward the red side of the spectrum. — At high brightness, InGaN red micro-LEDs can shift toward a higher frequency orange or yellow tone, known as blueshift. Image: Mena Davidson

To address the color instability, Xiao led an effort to develop a nanostructure that limits the source of the blueshift, and is working on a red micro-LED model that uses intrinsic crystal photonic effects to eliminate blueshift entirely.

“Our device emits red even under a current injection level two orders of magnitude greater than its optimal operating point, rendering the implementation of a RGB display solely based on III-nitride micro-LEDs an imminent possibility,” said Xiao, “This device structure also lays the foundation for the first InGaN based red emitting lasers. These developments will be the cornerstones for the next generation of highly efficient and ultra-small scale display applications.”

Xiao has previously been awarded the National Society Foundation Graduate Research Fellowship (NSF GRFP), as well as scholarships from Society of Vacuum Coaters Foundation (SVCF), AVS: Science and Technology of Materials, Interfaces, and Processing, and SPIE, the international society for optics and photonics.

Some IP related to this work has been licensed to NS Nanotech, Inc., which was co-founded by Z. Mi. The University of Michigan and Mi have a financial interest in the company.