Thermally stable and conductive nickel-incorporated gallium oxide thin-film electrode for efficient GaN microscale light-emitting diode arrays

Microscale light-emitting diodes (µLEDs) have attracted considerable attention as next-generation solid-state lighting sources owing to their reliable performance and attractive properties, such as easy miniaturization and stable operation in various movements. However, the quantum efficiency of μLEDs is lower than that of larger-size LEDs, which hinders their use in high-performance μLED display applications. Herein, a thermally stable and highly conductive GaOx thin-film as a p-type contact electrode is demonstrated by using electric-field-induced doping treatment (EDT) to achieve high-performance GaN µLEDs. The proposed GaOx electrode exhibits high transmittance (92%) and low specific contact resistance (3.5 × 10^-3 Ωcm²), along with high thermal stability (over 10 years at 77 °C). Transmission electron microscopy analyses show that conductive channels are formed in the GaOx electrode based on the diffusion of metallic Ni species from the top metal because of EDT, thereby facilitating efficient hole injection into the μLED pixels with little spreading to the passivation layers. Consequently, the µLED array with the GaOx electrode exhibited a 12% higher light output power and 57% higher current level than those of a µLED array with conventional ITO electrodes. The results of this study can guide efforts dedicated to further improving the performance of ITO-based optoelectronic devices, including µLEDs.