Investigation of sidewall passivation mechanism of InGaN-based blue microscale light-emitting diodes

Microscale light-emitting diodes (µLEDs) have been extensively employed for solid-state lighting applications. However, the ratio of the sidewall area to the emitting area increases as the pixel size of µLEDs decreases, which increases the non-radiative recombination probability on the sidewall surface and eventually degrades the performance of µLEDs. In this study, we investigate the nature of chemical bonds at the sidewall/passivation layer interface using three passivation materials (SiO₂, Al₂O₃, and Si₃N₄), to identify the underlying mechanism of passivation and thereby achieve high-performance InGaN-based µLEDs. According to the X-ray photoelectron spectroscopy results, the ratio of Ga[sbnd]O bonds on the sidewall/passivation layer interface to Ga[sbnd]N bonds varies with the passivation layer (1.1, 1.06, and 0.33 for SiO₂, Al₂O₃, and Si₃N₄, respectively). This amount is a key factor affecting the passivation and directly influences the µLED performance. The µLED with SiO₂ passivation exhibits a 39% higher light output power and 192% higher current density compared to those associated with the µLED with Si₃N₄ passivation. These results indicate that the suppression of non-radiative defects depends on the chemical states at the sidewall/passivation layer interface. The findings can provide guidance for optimizing the device performance of µLEDs by selecting appropriate passivation layers.