The 15th Global Conference on Materials Science and Engineering (CMSE 2026)

Abstract: Ultrawide-bandgap (UWBG) semiconductors, including AlN, BN, diamond, and Ga₂O₃, have attracted extensive research interest owing to their unique physical properties and broad potential applications in electronic and optoelectronic devices. Among these applications, microscale light-emitting diodes (μLEDs) have emerged as promising candidates for next-generation augmented reality and virtual reality displays. High-performance μLED displays require high pixel density, high efficiency, high brightness, excellent emission stability, and full-color capability. However, realizing full-color μLED displays remains challenging because conventional fabrication relies on the mass transfer and precise alignment of red, green, and blue μLED chips grown on different epitaxial wafers.

Rare-earth (RE)-doped semiconductors exhibit intense, spectrally narrow emissions arising from intra-4f electronic transitions of RE ions, making them attractive for color display and solid-state lighting applications. Considerable efforts have been devoted to developing visible-light emitters based on RE-doped GaN. It has been suggested that employing ultrawide-bandgap host materials can further enhance the luminescence efficiency of RE ions. We have demonstrated distinct red, green, and blue emissions from Eu-, Er-, and Tm-doped Ga₂O₃ thin films, respectively. Furthermore, the normalized emission intensities of RE-doped Ga₂O₃ exhibit significantly smaller temperature dependence than those of RE-doped GaN, indicating superior thermal stability. Optical luminescence studies provide valuable information on the electronic structure, host lattice, and defect states of semiconductors, thereby facilitating the optimization of crystal growth and material quality.

Synchrotron radiation is an ideal excitation source for investigating the optical properties of UWBG semiconductors because of its exceptionally high brightness and continuously tunable photon energy. To support such studies, we have established the Saga University Beamline (BL13) at the Saga Light Source (SAGA-LS), Japan, and developed a dedicated luminescence spectroscopy system. In this presentation, we will introduce the recent progress in our synchrotron radiation–based luminescence measurement system and present representative experimental results on rare-earth-doped ultrawide-bandgap semiconductors.

Biography: Prof. Dr. Guo received B.E., M.E., and Dr. Eng. degrees in Electronic Engineering from Toyohashi University of Technology, Japan, in 1990, 1992, and 1996, respectively. He is currently a Professor in the Department of Electrical and Electronic Engineering at Saga University, Japan. He also served as Director of the Saga University Synchrotron Light Application Center from April 2012 to March 2022. His research focuses on the epitaxial growth and characterization of semiconductor materials, particularly ultrawide-bandgap semiconductors for electronic and optoelectronic applications. He has authored and co-authored more than 400 scientific papers published in leading journals, including Nature Communications, Advanced Materials, Physical Review B, and Applied Physics Letters. His publications have received more than 12,500 citations, with an h-index of 56. He has been recognized among the World's Top 2% Scientists in the Stanford University ranking.