C. W. Kuo

High efficiency and improved ESD characteristics of GaN-based LEDs with naturally textured surface grown by MOCVD

The following paper presents a study on GaN-based light-emitting diodes (LEDs) with naturally textured surface grown by metal-organic chemical vapor deposition. The study utilizes a well-known approach of increasing light extraction efficiency. The approach is based on naturally formed V-shaped pits on surface that originate from low-temperature-growth (LTG) conditions of topmost p-GaN contact layer. In our experiment, the high-temperature-grown (HTG) p-GaN layer was inserted between the p-AlGaN electron-blocking layer and the LTG p-GaN contact layer, in order to suppress pit-related threading dislocations (TDs). These TDs may intersect the underlying active layer. The results of the experiment show that GaN-based LEDs with the HTG p-GaN insertion layer can effectively endure negative electrostatic discharge voltage of up to 7000 V. We also noted that application of 20-mA current injection yields output power of about 16 mW for the LEDs emitting around 465 nm. The output power results correspond to an external quantum efficiency of around 30%

Enhanced output power in GaN-based LEDs with naturally textured surface grown by MOCVD

GaN-based light-emitting diodes (LEDs) with naturally textured surfaces grown by MOCVD were demonstrated. In this study, a growth-interruption step and a surface treatment using biscyclopentadienyl magnesium (CP/sub 2/Mg) were simultaneously performed to form a plurality of nuclei sites on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface having truncated pyramids. Experimental results indicated that GaN-based LED with the truncated pyramids on the surface exhibited an enhancement in output power of 66% at 20 mA. It is worth noting that the typical 20-mA-driven forward voltage is only slightly higher than those of conventional LEDs (without the Mg-treatment process).

Nitride-based near-ultraviolet light emitting diodes with meshed p‐GaN

This investigation presents nitride-based near ultraviolet light emitting diodes (LEDs) with a meshed p‐GaN layer. With 20mA injection current, it was found that forward voltages were 3.33 and 3.39V while output powers were 9.0 and 10.6mW for the meshed indium-tin-oxide (ITO) LED and meshed p‐GaN LED, respectively. The larger LED output power is attributed to increased light extraction efficiency.

Optical Simulation and Fabrication of Nitride-Based LEDs With the Inverted Pyramid Sidewalls

In this study, the numerical and experimental demonstrations for the enhancement of light-extraction efficiency in nitride-based LEDs with randomly inverted pyramid sidewalls (IPSs) by chemical etching of the chip edge are presented. With 20 mA injection current, it was found that forward voltages were 3.69 and 3.75 V while output powers were 7.07 and 8.95 mW for the conventional LED and inverted pyramid sidewall LED, respectively. The larger LED output power is attributed to the increased light-extraction efficiency by IPSs.

Improvement of near-ultraviolet nitride-based light emitting diodes with mesh indium tin oxide contact layers

The authors have demonstrated nitride-based near-ultraviolet (NUV) light emitting diodes (LEDs) with mesh indium tin oxide (ITO) contact layer. With 20mA injection current, it was found that forward voltages were 3.94 and 4.05V while the output powers were 7.54 and 9.02mW for the planar ITO LED and mesh ITO LED, respectively. The larger LED output power should be attributed partially to the reduced absorption of ITO in the NUV region and partially to the better current spreading.

Dislocation reduction in GaN with multiple MgxNy∕GaN buffer layers by metal organic chemical vapor deposition

Unintentionally doped GaN epitaxial layers with a conventional single low temperature (LT) GaN buffer layer and with multiple MgxNy∕GaN buffer layers were grown on sapphire substrates by metal organic chemical vapor deposition. The multiple MgxNy∕GaN buffer layers exhibit a low nuclei density, increasing the volume of defect-free regions and reducing the dislocations associated with the grain boundaries. Therefore, the GaN with multiple MgxNy∕GaN buffer layers reveals an asymmetrical reflection (102) with a small full width at half maximum, and a higher mobility, lower background concentration, and lower etching pit density than the GaN with the LT GaN buffer layer.

Efficiency Improvement of GaN-Based Light-Emitting Diode Prepared on GaN Nanorod Template

We demonstrated the formation of GaN-based nanorod (NR) structure by using self-assemble Ni nanoislands as the etching mask. It was found that crystal quality of the GaN epilayer prepared on an NR GaN template was significantly better than that prepared with a conventional low-temperature GaN nucleation layer. With the NR GaN template, it was found that 20-mA light-emitting diode (LED) output power can be enhanced by 39.8%, as compared to the conventional LED.

GaN-Based Light-Emitting Diode Prepared on Nano-Inverted Pyramid GaN Template

Using self-aligned SiO2 nano-spheres as an etching mask, the authors demonstrated the formation of a GaN-based nano-inverted pyramid (NIP) structure. It was found that crystal quality of the GaN epilayer prepared on an NIP/GaN template was significantly better than that prepared with conventional low-temperature GaN nucleation layer. With the NIP structure, it was found that 20-mA light-emitting-diode (LED) output power can be enhanced by 32%, as compared with the conventional LED.

Improvement of the Efficiency of Nitride-Based Light Emitting Diodes on Nanoinverted Pyramid GaN Templates

In this study, we introduce a method combining the inductively coupled plasma and wet etching process with SiO 2 microspheres to fabricate the nanoinverted pyramid (NIP) structures of a GaN template. GaN epitaxial layers and GaN-based multiple quantum well light emitting diode (LED) structures with a conventional single GaN buffer and an NIP GaN template were proposed and fabricated. The NIP GaN template can significantly reduce dislocation density and thus improve the crystal quality of the GaN epitaxial layers. By using an NIP GaN template, we can enhance LED output power by 32%.

Four-Wavelengths-Mixed White Light Emitting Diodes with Dual-Wavelength-Pumped Green and Red Phosphors

The wavelengths of dual-wavelength light-emitting diodes (LEDs) are near ultraviolet (UV) at approximately 409 and 459 nm for blue when driven at 20 mA. The near-UV emission intensity of LEDs is stronger than the blue emission intensity with a 20 mA driven current. The green and red emission intensities of the phosphor are almost the same as, but less than, the blue emission intensity of the dual-wavelength LED with a 20 mA driven current. The CIE color coordinates are x=0.32 and y=0.35, while the dual-wavelength LED with a green and red phosphor LED lamp is driven at 20 mA.