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Light extraction for InGaN-based green thin-film micro-LEDs through surface roughening
Optics Express
|July 2, 2026
Summary
Surface roughening of indium gallium nitride (InGaN) micro-light-emitting diodes (micro-LEDs) with tetramethylammonium hydroxide (TMAH) improves light extraction. Larger micro-LEDs with bigger surface pyramids show higher efficiency, highlighting size-dependent performance.
Area of Science:
- Materials Science
- Optoelectronics
- Semiconductor Devices
Background:
- Indium gallium nitride (InGaN) micro-light-emitting diodes (micro-LEDs) are crucial for advanced micro-displays.
- Total internal reflection (TIR) significantly limits light extraction efficiency (LEE) in micro-LEDs.
- Surface roughening using alkaline solutions, like tetramethylammonium hydroxide (TMAH), is a key strategy to mitigate TIR.
Purpose of the Study:
- To investigate the impact of device size on the performance of TMAH-roughened InGaN micro-LEDs.
- To analyze the relationship between surface morphology, hexagonal pyramid size, and light extraction efficiency (LEE).
- To optimize surface roughening techniques for various micro-LED sizes.
Main Methods:
- Fabrication of green InGaN thin-film micro-LEDs on silicon substrates with sizes ranging from 14 to 54 µm.
- Surface roughening of the N-polarity n-GaN surface using tetramethylammonium hydroxide (TMAH).
- Characterization of external quantum efficiency (EQE) and surface morphology (hexagonal pyramid size) via experiments and finite difference time domain (FDTD) simulations.
Main Results:
- TMAH-roughened micro-LEDs showed size-dependent external quantum efficiency (EQE), with a 54 µm device achieving 24.20% and a 14 µm device achieving 13.18%.
- The average size of hexagonal pyramids formed by TMAH roughening increased with micro-LED device size.
- Finite difference time domain (FDTD) simulations confirmed that larger hexagonal pyramids correlate with higher light extraction efficiency (LEE).
Conclusions:
- Device size significantly influences the effectiveness of surface roughening for enhancing LEE in micro-LEDs.
- Optimizing surface morphology, specifically hexagonal pyramid size, is critical for maximizing LEE across different micro-LED dimensions.
- Future micro-LED design strategies must account for size-dependent surface characteristics to improve light extraction.
