Performance improvement of yellow flip-chip mini-LEDs via full-angle distributed Bragg reflector

Miniaturized light-emitting diodes (mini-LEDs) have gained much attention for liquid crystal displays back-light and self-emissive displays. However, the unsatisfactory performance of InGaN long-wavelength mini-LEDs hinders their practical applications. Herein, we develop a full-angle distributed Bragg reflector (DBR) and investigate its impact on the performance of yellow flip-chip mini-LEDs. The full-angle DBR consists of different stacks of Ti3O5/SiO2 layers that are optimized for multiple central wavelengths. Compared to conventional single-DBR stacks, such full-angle DBR enables wider reflectance bandwidth and less dependence of reflectance on the light incident angle from 0° to 50°. Specifically, full-angle DBR features high reflectance beyond 99% from 447 to 580 nm at an incident angle of 50°. Full-angle DBR is found to enhance the electric field intensity at the top of devices, indicating that light extraction efficiency is promoted. As a result, yellow flip-chip mini-LEDs with full-angle DBR show higher light output power than those without DBR at the same currents. Our work paves a way to improve the performance of small-size emitters with long wavelength.