Passivation to Improve the Efficiency and Reliability of III-Nitride Micro-Light-Emitting Diode

Abstract

Because group III-V and nitride-based micro light-emitting diodes (micro-LEDs) exhibit excellent performance, such as fast response, low power consumption, and thermal stability, they have been widely applied for display and biomedical applications, including optogenetics and multi-site neuron. However, unlike conventional LEDs (> 300 × 300 µm2), micro-LEDs (> 100 × 100 µm2) suffer from severe Shockley Read-Hall (SRH) non-radiative recombination, which is related to sidewall damage introduced by ICP-RIE dry-etching process for LED isolation. As the size of LEDs decreases, such non-radiative recombination phenomenon increases due to the increase in the sidewall surface ratio. Many attempts have been made to improve such defect-related recombination in micro-LEDs. In other words, sidewall passivation using dielectric materials was reported to be effective in alleviation sidewall-related leakage characteristics.In this study, we investigated the electrical and optical properties of GaN-based micro-LEDs (blue) as a function of the number of passivation layers. The passivation layers were deposited using plasma enhanced chemical vapor deposition (PECVD) or/and atomic layer deposition (ALD). It is shown that by employing combined deposition techniques of ALD and PECVD, the optical and electric performance of 10 µm-size micro-LEDs are significantly improved. Compared with the conventional PECVD passivation method, the combined ALD/PECVD passivation showed the smaller ideality factor. For the 10 µm-size micro-LEDs, maximum external quantum efficiency (EQE) was obtained at 35 A/cm2 when the stacked ALD/PECVD passivation layer was used, whereas it was attained at 79 A/cm2 when the PECVD passivation was used. Based on the emission microscopy results, leakage paths were observed. The results show that the use of stacked ALD/PECVD passivation layer could serve as a potentially important process for the fabrication of high-performance micro-LEDs (< 10 × 10 µm2).