GR-Th-P16 - Photoluminescence analysis of time-dependent isotropic dry etching for reducing sidewall nonradiative recombination of n-GaN in micro-LEDs

1. Growth
Zhengfei Wei1 , Sung-Jin Cho1, Andrew Newton1
1 Oxford Instruments Plasma Technology, Severn Beach, Bristol BS35 4GG, United Kingdom
Abstract text
 Micro-light-emitting diode (μLED) technology is emerging as a key solution for next-generation high-resolution displays, especially for augmented-reality (AR) and Virtual Reality (VR) applications. However, achieving highly efficient, ultra-small μLEDs remains a significant technical challenge due to strong non-radiative recombination at the sidewalls. This recombination, primarily attributed to Shockley-Read-Hall (SRH) defects arises from sidewall and surface damage induced during Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) process 1-3.

In this work, we demonstrate a significant improvement in photoluminescence (PL) intensity on n-type Gallium Nitride (n-GaN) surfaces by optimising the etch time of a damage-recovery isotopic dry etch following a mesa dry etching process. This treatment effectively removed the plasma-damaged layer formed on the surface of the nGaN during the mesa etching process. The damage is measured at the base of the etch rather than the masked mesa top. As a result, the average PL intensity exhibits an approximate 173% increase after 60 minutes-etching, compared with the n-GaN without isotropic etching. This enhancement is attributed to the reduction of SRH non-radiative recombination sites associated with sidewall and surface damage. Additionally, Kelvin probe force microscopy (KPFM) imaging revealed a progressive increase in surface potential with deeper isotropic etching, directly correlating with the observed improvement in PL intensity. To further understand this mechanism, we will use cathodeluminescence (CL) to investigate the role of strain relaxation and its interaction with sidewall surface non-radiative recombination, revealing their direct impact on the improvement of PL intensity. Furthermore, μLEDs currently being fabricated are expected to demonstrate a significant increase in external quantum efficiency (EQE). These advancements address critical obstacles in μLED fabrication and pave the way for a significant step towards commercialisation of μLED displays for AR/VR, phones and smart watches. 

References:

  1. X. Wang, et al. Nat Commun 14, 7569 (2023). 
  2. M. S. Wong et al 2019 Appl. Phys. Express 12 097004.
  3. M. Minami et al 2011 Jpn. J. Appl. Phys. 50 08JE03.