Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro-LEDs

Jeong Hwan Park, Markus Pristovsek, Wentao Cai, Heajeong Cheong, Atsushi Tanaka, Yuta Furusawa, Dong Pyo Han, Tae Yeon Seong, Hiroshi Amano

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)


The sidewall condition is a key factor determining the performance of micro-light emitting diodes (µLEDs). In this study, equilateral triangular III-nitride blue µLEDs are prepared with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions. It is found that inductively coupled plasma-reactive ion etching (ICP-RIE) causes surface damages to the sidewall and results in rough surface morphology. As confirmed by time-resolved photoluminescence (TRPL) and X-ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminates the etching damage and flattens the sidewall surface. After ICP-RIE, 100 µm2-µLEDs yield higher external quantum efficiency (EQE) than 400 µm2-µLEDs. However, after TMAH treatment, the peak EQE of 400 µm2-µLEDs increases by ≈10% in the low current regime, whereas that of 100 µm2-µLEDs slightly decreases by ≈3%. The EQE of the 100 µm2-µLEDs decreases after TMAH treatment although the internal quantum efficiency (IQE) increases. Further, the IQE of the 100 µm2-µLEDs before and after TMAH treatment is insignificant at temperatures below 150 K, above which it becomes considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non-radiative recombination rate and light extraction.

Original languageEnglish
Article number2203128
JournalAdvanced Optical Materials
Issue number10
Publication statusPublished - 2023 May 19

Bibliographical note

Funding Information:
This work was supported by the Global Research Laboratory (GRL) program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (NRF‐2017K1A1A2013160).

Publisher Copyright:
© 2023 Wiley-VCH GmbH.


  • external quantum efficiency
  • inductively coupled plasma-reactive ion etching
  • internal quantum efficiency
  • light extraction efficiency
  • micro-LEDs
  • sidewall conditions
  • tetramethylammonium hydroxide

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics


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