Improving the Leakage Characteristics and Efficiency of GaN-based Micro-Light-Emitting Diode with Optimized Passivation

We investigated the effect of atomic layer deposition (ALD) Al₂O₃ (50 nm)/plasma-enhanced chemical vapour deposition (PECVD) SiO₂ (250 nm) and PECVD SiO₂ (300 nm) passivation layers on the leakage current and efficiency of InGaN-based micro-LEDs with different sizes. Regardless of passivation layers, the leakage current increased with decreasing LED size and increasing reverse bias. Emission microscopy examination showed that with increasing reverse bias, the number of defect-related emission spots and their intensities increased. For the micro-LEDs <50 μm, the emission spots were mainly located at the sidewall regions. Above-10 V, the single PECVD SiO₂ passivation layer gave higher leakage current than the double ALD-Al₂O₃/PECVD-SiO₂ layer. The micro-LEDs with the single passivation layer gave the ideality factors of about 2.0, while that with the double layer exhibited values smaller than 2.0. The micro-LEDs with the double passivation layer exhibited external quantum efficiency peaks at lower current density compared to those with the single layer. It was shown that smaller micro-LEDs were more sensitively dependent on the types of the passivation layers. These results exhibit that the ALD-Al₂O₃/PECVD-SiO₂ passivation layer is more effective in suppressing the sidewall damage-induced current than the PECVD-SiO₂ layer.