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Full-angle DBR enhances flip-chip mini-LED performance


WHU team shows improved performance of flip-chip blue and green mini-LEDs by introducing a full-angle distributed Bragg reflector

Researchers from Wuhan University in China have proposed a novel full-angle Ti3O5/SiO2 DBR to enhance the performance of flip-chip blue and green mini-LEDs.

“The full-angle DBR provides a promising strategy for the development of high-efficiency blue and green flip-chip mini-LEDs for display application.” said Shengjun Zhou, a professor at Wuhan University who directed the research.

Mini-LEDs have been considered as one of the most promising candidates for next generation displays, due to their advantages of high brightness, high color saturation, power saving, and long lifetime. Mini-LEDs have significant potential as local dimming backlight unit in LCDs to realise high dynamic range (HDR). However, to realise the HDR requirement of LCDs, mini-LEDs should be more efficient.

In the study, published in the journal Optics Express, the researchers demonstrated full-angle Ti3O5/SiO2 DBR to improve the light output power of blue and green flip-chip mini-LEDs. The full-angle DBR, consisting of different DBR stacks optimized for discrete central wavelength in blue, green, and red wavelength region, could alleviate angular dependence and broaden reflective bandwidth in comparison with conventional DBRs.

Furthermore, the researchers fabricated two types of blue and green flip-chip mini-LEDs with highly reflective indium-tin oxide (ITO)/DBR and Ag/TiW p-type ohmic contacts. Compared with Ag/TiW, the ITO/DBR exhibits higher reflectivity in the light wavelength range of 420 to 580 nm as the incident angle of light increases from 0° to 60°.

As a result, improvements of ∼7.7 percent and ∼7.3 percent in light output powers of blue and green flip-chip mini-LEDs with ITO/DBR are attained with respect to that of blue and green flip-chip mini-LEDs with Ag/TiW under an injection current of 10 mA. In addition, the full-angle DBR also improves light intensity in side direction of flip-chip mini-LEDs, which is beneficial for mixing light in backlight system of LCDs.

‘Enhanced performance of GaN-based visible flip-chip mini-LEDs with highly reflective full-angle distributed Bragg reflectors’ by Lang Shi et al; Optics Express, 29(25): 42276-42286 (2021)

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