Kang-Yuan Lee

High extraction efficiency GaN-based light-emitting diodes on embedded SiO2 nanorod array and nanoscale patterned sapphire substrate

In this paper, GaN-based LEDs with a nanoscale patterned sapphire substrate (NPSS) and a SiO2 photonic quasicrystal (PQC) structure on an n-GaN layer using nanoimprint lithography are fabricated and investigated. The light output power of LED with a NPSS and a SiO2 PQC structure on an n-GaN layer was 48% greater than that of conventional LED. Strong enhancement in output power is attributed to better epitaxial quality and higher reflectance resulted from NPSS and PQC structures. Transmission electron microscopy images reveal that threading dislocations are blocked or bended in the vicinities of NPSS layer. These results provide promising potential to increase output power for commercial light emitting devices.

Enhanced light output power of GaN-based vertical-injection light-emitting diodes with a 12-fold photonic quasi-crystal by nano-imprint lithography

GaN-based thin-film vertical-injection light-emitting diodes (VLEDs) with a 12-fold photonic quasi-crystal (PQC) by nano-imprint lithography (NIL) are fabricated and presented. At a driving current of 20 mA and with a chip size of 350 μm × 350 μm, the light output power of our thin-film LED with a 12-fold PQC structure reaches 41 mW. This result is an enhancement of 78% when compared with the output power of a VLED without a PQC structure. In addition, the corresponding light radiation pattern shows a narrower beam shape due to the strong guided light extraction effect by the formed PQC structure in the vertical direction. (Some figures in this article are in colour only in the electronic version)

Enhancement of light output power of GaN-based light-emitting diodes using a SiO(2) nano-scale structure on a p-GaN surface

GaN (gallium nitride)-based light-emitting diodes (LEDs) with a nano-scale SiO2 structure between a transparent indium-tin oxide (ITO) layer and p-GaN were fabricated. The forward voltage at 20 mA for a GaN-based LED with a SiO2 nano-scale structure was slightly higher than that of a conventional GaN-based LED because the total area of the p-type metal contact between the transparent ITO layer and p-GaN was smaller. However, the light output power for the GaN-based LED with a nano-scale structured SiO2 at 20 mA was 24% higher than that for a conventional GaN-based LED structure. This increase in the light output power is mostly attributed to the scattering of light from the SiO2 photonic quasi-crystal (PQC) layer.

Improved Light Output Power of GaN-Based Light-Emitting Diodes Using Double Photonic Quasi-Crystal Patterns

The enhancement of light extraction from GaN-based light-emitting diodes (LEDs) with a double 12-fold photonic quasi-crystal (PQC) structure using nanoimprint lithography is presented. At a driving current of 20 mA on a transistor-outline-can package, the light output power of an LED with a nanohole patterned sapphire substrate (NHPSS) and an LED with a double PQC structure are enhanced by 34% and 61%, compared with the conventional LED. In addition, the higher output power of the LED with the double PQC structure is due to better reflectance on NHPSS and higher scattering effect on p-GaN surface using a 12-fold PQC structure pattern. These results provide promising potential to increase the output powers of commercial light-emitting devices.

Enhanced Light Output Power and Growth Mechanism of GaN-Based Light-Emitting Diodes Grown on Cone-Shaped

In this study, we successfully transferred the patterns of a cone-shaped patterned sapphire substrate (CPSS) into SiO2 layer to fabricate a cone-shaped SiO2 patterned template by using nanoimprint lithography (NIL). The GaN-based light-emitting diodes (LEDs) were grown on this template by metal-organic chemical vapor deposition (MOCVD). The transmission electron microscopy (TEM) images suggest that the stacking faults formed near the cone-shaped SiO2 patterns during the epitaxial lateral overgrowth (ELOG) can effectively suppress the threading dislocations, which results in an enhancement of internal quantum efficiency. The Monte Carlo ray-tracing simulation reveals that the light extraction efficiency of the LED grown on cone-shaped SiO2 patterned template can be enhanced as compared with the LED grown on CPSS. As a result, the light output power of the LED grown on cone-shaped SiO2 patterned template outperformed the LED grown on CPSS.

{\hbox{SiO}}_{2}

In this paper, we demonstrated the high performance GaN-based LEDs by using a high aspect ratio cone-shape nano-patterned sapphire substrate (HAR-NPSS). We utilized nano-imprint lithography (NIL) and dry-etching system to fabricate a high depth HAR-NPSS. The micro-scale patterned sapphire substrate (PSS) was also used for comparison. A great enhancement of light output was observed when GaN-based LEDs were grown on a HAR-NPSS or a PSS. The light output power of LEDs with a HAR-NPSS and LEDs with a PSS were enhanced of 49 and 38% compared to LEDs with a unpatterned sapphire substrate. The high output power of the LED with a HAR-NPSS indicated that the technology of NAR-NPSS not only can improve the crystalline quality of GaN-based LEDs but also a promising development to a NPSS.

Patterned Template

GaN-based thin-film vertical-injection light-emitting diodes (VLEDs) with a double 12-fold photonic quasi-crystal (PQC) structure formed using nanoimprint lithography (NIL) and inductively coupled plasma reactive-ion etching (ICP-RIE) are fabricated and presented. At a driving current of 20 mA and with a chip size of 350 350 mm2, our thin-film LED with a double-12-fold-PQC structure gave a light output power of 40.5 mW, which is an increase of 77% when compared with the output power of a VLED without a PQC structure at a peak wavelength of 460 nm. In addition, the corresponding light radiation patterns show a narrow beam shape due to the strong guided light extraction on the n-GaN surface and the reflected light effect of the PQC structure formed in the vertical direction on the p-GaN surface. # 2010 The Japan Society of Applied Physics

Investigation and Comparison of the GaN-Based Light-Emitting Diodes Grown on High Aspect Ratio Nano-Cone and General Micro-Cone Patterned Sapphire Substrate

Colloidal quantum dots (QDs) have emerged as promising color conversion light emitters for solid-state lighting applications [Nat. Photonics7, 13 (2012)NPAHBY1749-488510.1038/nphoton.2012.328 due to their emission tunability and near-unity photoluminescence quantum yields. In the current commercial LEDs, QDs are dispersed into an encapsulation layer in a far-field architecture, where the majority of the light emitted by the LED remains trapped within the epitaxy due to total internal reflection, drastically reducing the out-coupling efficiency. In this paper, we demonstrate a photonic quasi-crystal hybrid LED geometry that allows QD emitters to be placed in close proximity to the multiple quantum wells (MQWs) of the active area. This architecture greatly improves the coupling between MQWs and QDs, simultaneously allowing for a non-radiative resonant energy transfer between the MQWs and the QDs and near-field radiative coupling of trapped (guided) modes in the LED to the emitters. In this configuration, we demonstrate record-breaking effective quantum yields reaching 123% for single-color conversion LEDs and 110% for white light-emitting devices.