Enhanced light extraction efficiency of UV LEDs by encapsulation with UV-transparent silicone resin

Abstract

Increase of light extraction efficiency (LEE) and total output power of UV LEDs emitting at 265 nm and 310 nm, respectively, after encapsulation with a UV-transparent silicone are studied. Raytracing simulations suggest that a properly placed hemispherical encapsulation with a refractive index in the range from 1.4 to 1.8 enhances the LEE from 8% to up to 16% for flip-chip mounted UV LEDs with non-reflective metal contacts. The simulations also show that the absorption coefficient of the encapsulant determines the maximum LEE and optimum dome diameter and that it should be below 3 cm-1. The silicone encapsulant exhibits a refractive index of 1.47 (1.45) and an absorption coefficient of 1.3 cm-1 (0.47 cm-1) at 265 nm (310 nm). AlGaN/sapphire-based UVC and UVB LED chips were flip-chip mounted on planar AlN ceramic packages and encapsulated with a 1.5 mm-radius hemispherical silicone dome. The total output power at an operation current of 350 mA increased from 27 mW to 46 mW for 265 nm LEDs and from 45 mW to 78 mW for 310 nm LEDs. This corresponds to an enhancement of about 70%, which agrees with the simulations. Moreover, far-field measurements of encapsulated LEDs showed a narrowing of the emission cone.

AlGaN/AlN Stranski–Krastanov Quantum Dots for Highly Efficient Electron Beam-Pumped Emitters: The Role of Miniaturization and Composition to Attain Far UV-C Emission

“…For electron beam-pumped lamps with transmission geometry, encapsulation with a hemispherical silicone dome could also be a viable option to improve light extraction. 49 Another important consideration is thermal management. Several experiments, including those conducted by Ivanov et al (up to 60 mW emission), 11 Jmerik et al (up to 150 mW), 38 and Rong et al (up to 2.2 W), 39 have shown a significant improvement of the efficiency (by almost a factor of 2) under pulsed excitation.…”

“…However, integrating an Al-based mount as a reflector can be crucial, and the use of patterned sapphire substrates promises an important improvement. For electron beam-pumped lamps with transmission geometry, encapsulation with a hemispherical silicone dome could also be a viable option to improve light extraction …”

Radiative Recombination and Carrier Injection Efficiencies in 265 nm Deep Ultraviolet Light‐Emitting Diodes Grown on AlN/Sapphire Templates with Different Defect Densities

“…For this purpose, the LEDs on the wafer were diced and flip‐chip mounted on AlN ceramic packages, as shown in Figure 3d. The best performing device ( = 35%) was then encapsulated by a UV‐transparent silicone resin “Deep UV200,” [ 30 ] as shown inFigure 3e. The MQW region area ( A ) of the mounted devices ( A = 5.7 × 10 −7 m 2 ) differs from that of DUV LEDs measured on‐wafer ( A = 1.5 × 10 −7 m 2 ).…”

Enhancement of Light Efficiency of Deep-Ultraviolet Light-Emitting Diodes by Encapsulation with a 3D Photonic Crystal Reflecting Layer

“…Unfortunately, UVC LEDs are limited by epitaxial and packaging technologies; consequently, commercial UVC LEDs mostly exhibit low external quantum efficiency and light output power (LOP), greatly limiting their applications [ 5 ]. Therefore, improving the light output efficiency (LOE) of UVC LEDs is crucial [ 6 , 7 , 8 ].…”