Enhancement of the light extraction characteristics and wide-angle emissive behavior of deep-ultraviolet flip-chip light-emitting diodes by using optimized optical films

We propose the use of optical films to enhance the light extraction efficiency (LEE) and wide-angle emission of traditional packaged deep-ultraviolet light-emitting diodes (DUV-LEDs). Total internal reflection occurs easily in DUV-LEDs because they contain sapphire, which has a high refractive index. DUV-LEDs also contain an aluminum nitride (AlN) ceramic substrate, which has high light absorption in the ultraviolet band. Photons are absorbed by the sapphire and AlN ceramic substrate, which reduces the LEE of DUV-LEDs. By adding a brightness enhancement film (BEF) on the sapphire surface and a high-reflection film (HRF) on the surface of the AlN ceramic substrate, the LEE of DUV-LEDs can be increased. Moreover, we designed a single-layer metal reflective film (SMRF) on the upper surface of the quartz glass in order to achieve wide-angle emission. Experimental results indicated that compared with traditional packaged DUV-LEDs, the light output power and external quantum efficiency of DUV-LEDs with a plated BEF, HRF, and SMRF increased by 18.3% and 18.2%, respectively. Moreover, an emission angle of 160° was achieved. In a reliability test, DUV-LEDs maintained more than 95% of the initial forward voltage and light output power after 1000 h of operation at 25°C, which indicated that the addition of an optical film can improve the light efficiency and long-term reliability of DUV-LEDs.

Effect of quartz lens structure on the optical performances of near-ultraviolet light-emitting diodes

Near-ultraviolet light-emitting diodes (NUV-LEDs) have been a rising UV light source for identification, resin curing, ink-printing, and illumination. In pursuit of more extensive application in different fields, their optical performances are obliged to be better. In this paper, we investigated the effect of a quartz lens structure on the optical performances of NUV-LEDs. The feature size of the quartz lens was optimized by optical simulations. When the quartz lens has the optimized feature size with a height above 1.8 mm while adding a silicone layer between the chip and the lens, the NUV-LEDs achieve the highest light efficiency, and exhibit a smallest light spot and largest light energy at the center region. Furthermore, different lenses were prepared and applied in the packaging of NUV-LEDs. As a consequence, the light output power of NUV-LEDs with a silicone layer is enhanced by 20.19% at the current of 220 mA. The light output power of NUV-LEDs is enhanced by 38.66%, 43.98%, and 53.30%, respectively, by using the different quartz lenses at the current of 220 mA, and the NUV-LED achieves the highest luminous intensity by 0.098 cd and smallest output light angle by 106.0°. It is attributed to the significant refraction effect of the quartz lens, which improves the optical performances of NUV-LEDs.

Bio-Inspired Flexible Fluoropolymer Film for All-Mode Light Extraction Enhancement

Enhancing the light extraction efficiency is a prevalent but vital challenge for most solid-state lighting technologies, especially for deep ultraviolet light-emitting diodes (DUV-LEDs). In this paper, inspired by the microstructure of the butterfly's eye, we propose and fabricate a flexible fluoropolymer film (FFP film) to tackle this issue for all-mode, full-wavelength light extraction enhancement for most solid-state lighting technologies compatibly. The experimental results demonstrate that compared with one mounted with a smooth FFP film, the light output power of DUV-LED is enhanced up to 26.7% by mounting the FFP film with 325 nm radius nanocones at a driving current of 200 mA. Importantly, thanks to the super-flexible feature of the FFP film, it can both cover the top surface and sidewalls of the DUV-LED chip, leading to the improvement of transverse electric and transverse magnetic mode light extraction by 20.5 and 21.8%, respectively. Finite element analysis (FEA) simulations of the electric field distribution of DUV-LEDs with the FFP film reveal the underlying physics. The present strategy is proposed from the view of the packaging level, which is cost-effective, able to be manufactured at a large scale, and compatible with the solid-state lighting technologies.

Enhancing the Light-Extraction Efficiency of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes by Optimizing the Diameter and Tilt of the Aluminum Sidewall

To realize high-efficiency AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs), enhancing their light-extraction efficiency (LEE) is crucial. This paper proposes an aluminum-based sidewall reflector structure that could replace the conventional ceramic-based packaging method. We design optimization simulations and experimental results demonstrated the light power output could be enhanced 18.38% of DUV-LEDs packaged with the aluminum-based sidewall.

Enhanced light extraction of deep ultraviolet light-emitting diodes by using optimized aluminum reflector

Deep ultraviolet light-emitting diodes (DUV-LEDs) have become a promising UV light source for sterilization, disinfection, and purification. However, the challenge in practical application of DUV-LEDs still remains in their low light efficiency. In this paper, we propose an optimized aluminum (Al) reflector for the light extraction enhancement of DUV-LEDs. The optical model of DUV-LEDs was established, and the optical simulations were performed to achieve the optimized reflector. The DUV-LEDs exhibit the highest light efficiency when the reflector has the optimized feature sizes with an angle of 60°, a height of 2.0 mm, and an internal radius of 2.5 mm. Furthermore, the optimized reflector with different reflectance was fabricated and applied for the packaging of DUV-LEDs. Consequently, the light output powers of DUV-LEDs are enhanced by 28.8%, 37.0%, and 43.8%, respectively, by using the different reflectors at the driving current of 100 mA. It is attributed to the remarkable reflection effect of the Al reflector, which increases the light extraction of the sidewall emission from the DUV-LED chip.