A research team led by Professor Do Young Rag from the Department of Chemistry at Kookmin University (President Jeong Seung Ryul) has presented a new fundamental technology to solve a major challenge in the field of ultra-small micro/nano LEDs (micro-/nano-LEDs), a technology gaining attention as a core component for next-generation displays. The team demonstrated that introducing UV-irradiated moisture adsorption (UVIMA) surface control technology into a top-down nanofabrication-based Fin-LED structure fundamentally improves the critical efficiency degradation problem previously considered inevitable in ultra-small LEDs under 5 μm.

Micro/nano LEDs are regarded as next-generation display technology offering higher brightness, longer lifespan, and superior energy efficiency compared to organic light-emitting diode (OLED). However, as chip sizes shrink below several micrometers, non-radiative recombination increases due to Shockley–Read–Hall (SRH) defects and dangling bonds on the surface during dry etching processes, causing a sharp decline in luminous efficiency.
Conventional passivation based on inorganic SiO₂·Al₂O₃ nanofilm coatings effectively mitigated some SRH defects but failed to provide a fundamental solution for the most critical dangling bond issue, remaining a major hurdle for commercializing ultra-small LEDs below 5 μm.

The research team newly designed a sequential nanofabrication process combining low-damage dry etching–wet etching–UVIMA. Crucially, the UVIMA process photochemically activates moisture in the air during ultraviolet irradiation, chemically adsorbing it onto the LED surface. This effectively stabilizes dangling bonds formed during etching.
This process activates the delayed luminescence mechanism, rarely utilized in existing GaN-based micro/nano LEDs. It converts electrons trapped in SRH defects and dangling bonds—previously considered non-radiative losses—into pathways contributing to luminescence.

The research team experimentally demonstrated, through time-resolved photoluminescence (TRPL) and temperature-dependent photoluminescence (TDPL) analysis along with various crystallographic analyses, that defects can be transformed from mere loss sources into elements contributing to enhanced luminescence efficiency.
As a result, in sub-5 μm micro/nano-sized InGaN/GaN Fin-LEDs, they achieved an internal quantum efficiency of 70.9%, an external quantum efficiency of 16.5%, and an electroluminescence luminance of approximately 18,000 cd/m², demonstrating that ultra-miniature micro LEDs have reached a performance level suitable for industrial applications.

Furthermore, the Fin-LED structure enables aligned placement on electrodes via dielectrophoretic assembly technology, securing scalability for ultra-high-resolution pixel manufacturing processes. The research team experimentally confirmed the potential for high-resolution display applications, including wristwatch and automotive displays, by implementing a 64×64 sub-pixel passive matrix image.

Professor Do Young Rag stated, “The performance limitations of ultra-miniature LEDs stem from SRH surface defects and dangling bonds arising in microfabrication processes.” He added, “This research is significant because it demonstrates that commercial-level efficiency can be achieved even in micro/nano LEDs by utilizing the physical mechanism of delayed luminescence through UV and water-based photochemical surface control technology.”

Dr. Lee Seung Jae from the Department of Chemistry at Kookmin University participated as the first author. The Korea Electronics Technology Institute, Kyung Hee University, and Hongik University collaborated as co-research institutions. The research findings were published online in the prestigious international journal Nano Energy and were supported by the National Research Foundation of Korea and the Korea Planning & Evaluation Institute of Industrial Technology (KEIT).

This achievement represents a nano-process-based optical technology platform that resolves the efficiency degradation issue—the primary obstacle for micro/nano LED displays under 5 μm—at the mechanism level. It is anticipated to serve as a core foundational technology accelerating the low-cost, high-efficiency commercialization of micro/nano-LEDs across the entire high-resolution inorganic light-emitting display and next-generation panel industries.