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

With the development of single-photon-sources of ultra-efficient light extraction, nanowire structures, with embedded quantum wells, present unprecedented opportunity to enhance the light extraction efficiency (LEE) of light emitting diodes (LEDs). In this paper, the finite-difference time-domain method is carried out in graphics processing units to explore mechanisms by which nanowire arrays can effectively improve LEE. The results show that the LEE strongly depends on the radius of the nanowire and the distance between the nanowires. On analyzing the emitted power distribution of the dipole in the semiconductor nanowire, the LEE of LEDs agrees with guided power portion of the total power with respect to the radius of the nanowire and the distance between the nanowires. The guided mode has an important role in enhancing the LEE of LEDs. The free-space mode, however, becomes the whispering gallery mode which is not important in LEE. The LEE obtains the maximum at the mode cutoff radius. The height is also discussed in this paper. With the optimized parameters, ~11 times increment in LEE is achieved.

Analysis on the Light Extraction Efficiency of GaN-Based Nanowires Light-Emitting Diodes

Study on Light Extraction from GaN-based Green Light-Emitting Diodes Using Anodic Aluminum Oxide Pattern and Nanoimprint Lithography

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Study on Light Extraction from GaN-based Green Light-Emitting Diodes Using Anodic Aluminum Oxide Pattern and Nanoimprint Lithography.

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

This study systematically investigates the light-extraction efficiency (LEE) of GaN-based thin-film flip-chip light-emitting diodes (TFFC LEDs) with deeply etched photonic crystals (PhC). The optimal structure can be obtained by scanning the structural parameters using a three-dimensional finite-difference time-domain simulation. The concentration of the internal emission pattern within a limited extraction cone is significantly influenced by several structural parameters. The light-collection enhancement within an extraction cone explains the peak LEE caused by optimized structural parameters such as the p-GaN thickness, the air-hole depth, the lattice constant and the filling factor. The maximum extraction efficiency can reach 65% in the case of a p-GaN thickness of 140 nm, air-hole depth of 240 nm, lattice constant of 350 nm and filling factor of 0.40. Additionally, fabricating the optimal electrical contacts on the planar top surface of the n side can contribute to a higher potential enhancement.

Improving the Vertical Light-Extraction Efficiency of GaN-Based Thin-Film Flip-Chip LEDs With p-Side Deep-Hole Photonic Crystals

The interaction of low-order modes with photonic crystals (PhCs) has been a promising technique to increase light extraction efficiency (LEE) of LEDs. In this paper, numerical simulations based on the finite-difference time-domain method were carried out to explore different mechanisms that can effectively improve this interaction. The results showed that deeply etched PhCs have inefficient light extraction since they would decrease the effective thickness of the unetched layer and cut off some guided modes. By applying the AlxGa1-xN confining layer, the distribution of guided modes was changed. The cap layer mode was isolated from the GaN buffer, and larger LEE was achieved. Furthermore, dramatic increments with oscillations were found in the LEE by using embedded PhCs. Resonances of the Bloch mode localized within these PhCs, which caused the oscillations, were further modified by a shallow AlxGa1-xN confining layer. With the optimized parameters, over eightfold increment in LEE was achieved. In addition, dislocations caused by higher Al content and thicker AlxGa1-xN layer were avoided. This proposed structure could be a very promising candidate for high extraction efficiency LEDs.

Improving Light Extraction Efficiency of GaN-Based LEDs by Al $_{\bm x}$ Ga $_{{\bf 1}{\bm -}{\bm x}}$ N Confining Layer and Embedded Photonic Crystals

Xinlian Chen

Papers

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

Improving the Vertical Light-Extraction Efficiency of GaN-Based Thin-Film Flip-Chip LEDs With p-Side Deep-Hole Photonic Crystals

Improving Light Extraction Efficiency of GaN-Based LEDs by Al $_{\bm x}$ Ga $_{{\bf 1}{\bm -}{\bm x}}$ N Confining Layer and Embedded Photonic Crystals