We report a zirconium-phenyl siloxane hybrid material (ZPH) that can be used as a robust LED encapsulant. The ZPH encapsulant was fabricated via hydrosilylation-curing of sol–gel derived multifunctional (vinyl- and hydride-functions) siloxane resins containing phenyl-groups and Zr–O–Si heterometallic phase for achieving a high refractive index (n ≈ 1.58). In thermal aging, the ZPH LED encapsulant exhibited superior performances with a high optical transparency (∼88% at 450 nm) and exhibited high thermal stability (no yellowing at 180 °C for 1008 h), compared to a commercial LED encapsulant (OE-6630, Dow Corning Corporation). This suggests potential for ZPH to be a robust LED encapsulant.

Sol–Gel Derived Transparent Zirconium-Phenyl Siloxane Hybrid for Robust High Refractive Index LED Encapsulant

Due to the excellent optoelectronic properties, fast response time, outstanding power efficiency and high stability, micro-LED plays an increasingly important role in the new generation of display technology compared with LCD and OLED display. This paper mainly introduces the preparation methods of the GaN-based micro-LED array, the optoelectronic characteristics, and several key technologies to achieve full-color display, such as transfer printing, color conversion by quantum dot and local strain engineering.

https://iopscience.iop.org/article/10.1088/1674-4926/41/4/041606/pdf

Characteristics and techniques of GaN-based micro-LEDs for application in next-generation display

We demonstrate GaN-based double-layer electrode flip-chip light-emitting diodes (DLE-FCLED) with highly reflective indium-tin oxide (ITO)/distributed bragg reflector (DBR) p-type contact and via hole-based n-type contacts. Transparent thin ITO in combination with TiO2/SiO2 DBR is used for reflective p-type ohmic contact, resulting in a significant reduction in absorption of light by opaque metal electrodes. The finely distributed via hole-based n-type contacts are formed on the n-GaN layer by etching via holes through p-GaN and multiple quantum well (MQW) active layer, leading to reduced lateral current spreading length, and hence alleviated current crowding effect. The forward voltage of the DLE-FCLED is 0.31 V lower than that of the top-emitting LED at 90 mA. The light output power of DLE-FCLED is 15.7% and 80.8% higher than that of top-emitting LED at 90 mA and 300 mA, respectively. Compared to top- emitting LED, the external quantum efficiency (EQE) of DLE-FCLED is enhanced by 15.4% and 132% at 90 mA and 300 mA, respectively. The maximum light output power of the DLE-FCLED obtained at 195.6 A/cm2 is 1.33 times larger than that of the top-emitting LED obtained at 93 A/cm2.

GaN-based flip-chip LEDs with highly reflective ITO/DBR p-type and via hole-based n-type contacts for enhanced current spreading and light extraction

Analysis on the effect of amorphous photonic crystals on light extraction efficiency enhancement for GaN-based thin-film-flip-chip light-emitting diodes

High power InGaN/GaN flip‐chip LEDs with via‐hole‐based two‐level metallization electrodes

Study of light extraction efficiency of flip-chip GaN-based LEDs with different periodic arrays

Although photonic crystals (PhCs) have been used to enhance the light extraction efficiency (LEE) of light emitting diodes (LEDs) in a lot of researches, the effects of PhCs on the electrical and optical characteristics of GaN-based high power LEDs have been rarely analyzed simultaneously. Herein, the 3D finite-element method (FEM) was employed to investigate the current density distribution in the active layer of LEDs while the LEE was calculated based on the finite-difference time-domain method. Then the influences of several parameters, including the radius, the filling factor, and the etching depth of PhCs on the current density distribution and external quantum efficiency (EQE) of LEDs were examined. It was found that the configurations of PhCs had a significant influence on the electrical and optical performances of LEDs. With the optimized parameters, a 62 % enhancement of EQE and more uniform current density distribution have been obtained comparing to those of LEDs with planar ITO. These analysis results can facilitate the identification of the design rules for high power, high efficiency LEDs.

Ming-yu Zhang

Papers

Study of light extraction efficiency of flip-chip GaN-based LEDs with different periodic arrays

Electrical-optical analysis of photonic crystals GaN-based high power light emitting diodes