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Wuhan team enhances DUV LED performance


Researchers improve 275 nm DUV LEDs with internal-roughed sapphire and SiO2-antireflection film

Researchers from Wuhan University and Ningbo ANN Semiconductor in China have reported the adoption of internal-roughed sapphire covered with SiO2-antireflection film to improve the light output power (LOP) of 275 nm AlGaN-based deep-ultraviolet LEDs.

“We reveal that the air hole structure of internal-roughed sapphire enhances light scattering to reduce total internal reflection, which favours high-angle light extraction. In addition, the SiO2-antireflection film favours low-angle light extraction due to the destructive interference of reflected light.” said Shengjun Zhou, a professor at Wuhan University who directed the research.

AlGaN-based DUVLEDs have a wide range of applications, including water purification, sterilization, deodorization, and sensing. However, the performance of AlGaN-based DUV LEDs is still far below that of commercial GaN-based blue LEDs.

The dominant transverse magnetic (TM) light in the active region of AlGaN-based DUV LEDs is polarised along the direction normal to the surface and propagates mainly in the lateral directions, resulting in low light extraction efficiency (LEE).

The researchers introduce internal-roughed sapphire substrate coated with SiO2-antireflection film to AlGaN-based DUV LEDs for LOP enhancement. Experimental results demonstrate that the LOP of the proposed DUV LED is enhanced by 20.85 percent at 350 mA, compared with conventional DUV LEDs.

Finite-difference time-domain numerical simulations reveal that the internal-roughed sapphire substrate significantly improved high-angle extraction, while the SiO2-antireflection film improved low-angle extraction. As a result, the LEE of TM polarised light in DUV LEDs is significantly improved.

'Enhanced performance of 275-nm AlGaN-based deep-ultraviolet LEDs via internal-roughed sapphire and SiO2-antireflection film' by Yinzuo Qian et al; Optics Letters, 48(4): 1072-1075 (2023).

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