Efficiency enhancement of AlGaInP-based red mini-LEDs by a HfO₂-based hybrid passivation layer

Owing to the low refractive index of conventional passivation materials and sidewall defects, AlGaInP-based red miniaturized light-emitting diodes (mini-LEDs) suffer from low light extraction efficiency (LEE) and external quantum efficiency (EQE). Here, we propose a HfO₂-based hybrid passivation layer comprising a 5-nm-thick atomic-layer-deposited (ALD) HfO₂ passivation layer, a 15-nm-thick ALD-Al₂O₃ passivation layer, and an 800-nm-thick plasma-enhanced-chemical-vapor-deposited SiO₂ passivation layer. Owing to a more compatible refractive index with that of AlGaInP, the HfO₂ could increase the light emission angle at the HfO₂/AlGaInP interface and thus improve the LEE of AlGaInP-based mini-LEDs. Simulation results indicate that mini-LEDs with an HfO₂-based hybrid passivation layer exhibit enhanced light output performance with a 15.1% increment in LEE. Furthermore, experimental results demonstrate that mini-LEDs with an HfO₂-based hybrid passivation layer achieve a peak EQE of 20.19% at 5 mA, representing an improvement of 6.7% in EQE compared to mini-LEDs without an HfO₂-based hybrid passivation layer. This work provides an HfO₂-based hybrid passivation layer as a scalable strategy for advancing high-performance mini-LEDs in next-generation display technologies.