<p>AlGaInP-based red miniaturized light-emitting diode (mini-LED) is a key component in realizing a full-color display. One of the main obstacles originates from interfacial recombination at the AlGaInP-SiO₂ interface, and it is crucial to develop effective surface passivation strategies to achieve higher external quantum efficiency (EQE) in AlGaInP-based red mini-LEDs. Here, we demonstrated AlGaInP-based red flip-chip mini-LEDs with an AlN passivation layer via atomic layer deposition (ALD). Utilizing a Monte Carlo ray tracing method, we investigated the effects of the SiO₂ passivation layer and the AlN passivation layer on the optical performances of mini-LEDs. Since the refractive index of AlN is between AlGaInP and SiO₂, the total internal reflection is alleviated and light extraction is enhanced. Unexpectedly, the AlN passivation layer also contributes to improving the current spreading ability of mini-LEDs, which is demonstrated by the near-field light distribution. Benefiting from superior light extraction and improved current spreading, the EQE of the mini-LED with an AlN passivation layer realizes an increment of 16.1% at 5 mA, in comparison to the mini-LED with a SiO₂ passivation layer. The EQE of mini-LEDs with an AlN passivation layer reaches a competitive value of 22.3% at 5 mA, surpassing previously reported AlGaInP-based red mini-LEDs. Moreover, the high temperature-humidity aging test exhibits that the AlN passivation layer effectively enhances the reliability of mini-LEDs. This work provides guidance for high-performance AlGaInP-based red flip-chip miniLEDs design and manufacture.</p>