Z Ma

Tunable clover-shaped GaN photonic bandgap structures patterned by dual-step nanosphere lithography

The fabrication of close-packed clover-shaped photonic crystal structure on GaN by dual-step nanosphere lithography is demonstrated. By shrinkage of spheres prior to pattern transfer, a non-closed-packed clover-shaped photonic bandgap (PBG) structure, as designed by modified 3D finite-difference time-domain simulation, is also realized. The PBG of the close-packed and non-close-packed clover-shaped structures is verified through optical transmission spectroscopy, found to agree well with simulated results. A threefold enhancement in photoluminescence (PL) intensity is observed from the optimized structure, when the PBG is tuned to overlap with the emission band of the InGaN/GaN multi-quantum wells. From time-resolved PL measurements, shortened decay lifetimes are observed.

Plasmonically enhanced quantum-dot white-light InGaN light-emitting diode

The enhancement of white light emission from quantum-dot-coated InGaN light-emitting diodes (LEDs) via localized surface plasmon (LSP) resonance of metallic nanoparticles (MNPs) is investigated and demonstrated. With liquid-immersion laser ablation of metals, MNPs with a broad range of dimensions were synthesized in a single process. Since the LSP resonant wavelength depends strongly on the dimensions of MNPs, enhancement over a wide range of wavelengths in the visible spectrum is expected. MNPs of Ag, Au, Cu, Ni and Ti were experimented on. It is found that all MNPs result in an increase in the luminous flux and luminous efficacy of the quantum-dot-coated LEDs, with Ag NPs having the strongest effect (17.9%) amongst all metals tested. This observation is explained in terms of the resonance of the polarizability of the MNPs.

Vertically Mounted InGaN-on-Sapphire Light-Emitting Diodes

An InGaN/GaN light-emitting diode (LED) chip mounted in a vertical configuration (vmLED) is demonstrated, exhibiting significant enhancement to light extraction, compared with a LED mounted in a conventional planar geometry. By flipping the chip orthogonally, two large illumination surfaces of the device are exposed for direct light extraction. Comparisons, through ray-trace modeling and experiment data with conventional surface-mounted LEDs, indicate that the vmLEDs achieve superior light extraction efficiency. A sapphire-prism-mounted vmLED is further proposed to improve heat sinking, which is well suited for higher current operations.

Colour tuneable LEDs

Abstract: Light-emitting diodes are inherently monochromatic light sources. However, owing to their miniature footprints, color-mixing using these devices is much more feasible compared to conventional light sources, which are many times larger in size. The ability to mix colors offers the capability of color-tuning in real time without the use of color filters. Two types are color-tunable LEDs are described in this chapter: red-green-blue stacked LEDs suitable for high-power applications and group-addressable micro-LED arrays with jet-printed red-green blue micro-pixels, suitable for monolithic integration.

Color tunable LEDs

Abstract: Light-emitting diodes are inherently monochromatic light sources. However, owing to their miniature footprints, color-mixing using these devices is much more feasible compared to conventional light sources, which are many times larger in size. The ability to mix colors offers the capability of color-tuning in real time without the use of color filters. Two types are color-tunable LEDs are described in this chapter: red-green-blue stacked LEDs suitable for high-power applications and group-addressable micro-LED arrays with jet-printed red-green blue micro-pixels, suitable for monolithic integration.

13 – Color tunable LEDs

Abstract: Light-emitting diodes are inherently monochromatic light sources. However, owing to their miniature footprints, color-mixing using these devices is much more feasible compared to conventional light sources, which are many times larger in size. The ability to mix colors offers the capability of color-tuning in real time without the use of color filters. Two types are color-tunable LEDs are described in this chapter: red-green-blue stacked LEDs suitable for high-power applications and group-addressable micro-LED arrays with jet-printed red-green blue micro-pixels, suitable for monolithic integration.