Li-Chuan Chang

Spatial Correlation Between Efficiency and Crystal Structure in GaN-Based Light-Emitting Diodes Prepared on High-Aspect Ratio Patterned Sapphire Substrate With Sputtered AlN Nucleation Layer

In this paper, we investigate sputtered physical vapor deposition (PVD) AlN nucleation layer effects on crystal quality and efficiency of GaN-based light-emitting diodes (LEDs) prepared on high-aspect ratio patterned sapphire substrate (HARPSS). The crystal quality of the GaN epitaxial layer prepared on HARPSS with a PVD AlN nucleation layer was significantly better than that with a conventional metal organic chemical vapor deposition (MOCVD)-grown AlN nucleation layer. In addition, the pure wurzite structure GaN prepared on HARPSS could be obtained using PVD AlN nucleation layer. With the PVD AlN nucleation layer, the 20-mA LED light output power of the LEDs can be enhanced by 47.7% compared with the LEDs with the conventional MOCVD-grown AlN nucleation 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.

Current Spreading Improvement in GaN-Based Light-Emitting Diode Grown on Nano-Rod GaN Template

In this letter, we demonstrate GaN-based light-emitting diodes (LEDs) with high-quality heavily-Si-doped n-GaN prepared on a nano-rod GaN (NR-GaN) template. With 20-mA current injection, it was found that light output power (LOP) can be enhanced 29.0%, as compared to the conventional LED. Enhancement of the LOP can be attributed to the improvement of the current spreading and the increase of light extraction efficiency by using the heavily-Si-doped n-GaN prepared on the NR-GaN template.

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.

Nitride-Based Blue Light-Emitting Diodes Grown With InN/GaN Matrix Quantum Wells

Nitride-based light-emitting diodes (LEDs) grown with a structure of InN/GaN matrix quantum-wells (QWs) using metal-organic chemical vapor deposition are fabricated and characterized. The InN/GaN matrix QWs can significantly enhance the formation of phase-separated In-rich regions. Under an injection current of 500 A/cm2, the LED output power can be enhanced by 26%, and the efficiency droop can be improved as compared with a conventional LED. These improvements could be attributed to the strong localization effect to remove carriers from the confining potential and capture these carriers at nonradiative centers in the active layer.

Regrowth of High Quality Heavily Si-Doped nGaN Utilizing Nano-Rod GaN Template

In this study, heavily Si-doped n-type GaN (n-GaN) epitaxial layers with and without nanorod GaN (NR GaN) template were grown by metal organic chemical vapor deposition (MOCVD) system. It was found that we could achieve high-qulaity heavily Sidoped n-GaN layers by using the NR GaN template. It was also found that we can reduce etching pits density in n-GaN (1.5E19 cm ) epitaxial layer by a factor of 2.82 using the NR GaN template, as compared to the conventional sapphire substrate. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3617533] All rights reserved.

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%.

Void Shapes Controlled by Using Interruption-Free Epitaxial Lateral Overgrowth of GaN Films on Patterned SiO2 AlN/Sapphire Template

GaN epitaxial layers with embedded air voids grown on patterned SiO2 AlN/sapphire templates were proposed. Using interruption-free epitaxial lateral overgrowth technology, we realized uninterrupted growth and controlled the shape of embedded air voids. These layers showed improved crystal quality using X-ray diffraction and measurement of etching pits density. Compared with conventional undoped-GaN film, the full width at half-maximum of the GaN (0 0 2) and (1 0 2) peaks decreased from 485 arcsec to 376 arcsec and from 600 arcsec to 322 arcsec, respectively. Transmission electron microscopy results showed that the coalesced GaN growth led to bending threading dislocation. We also proposed a growth model based on results of scanning electron microscopy.

GaN-Based Light-Emitting-Diode With a p-InGaN Layer

GaN-based LEDs with a p-InGaN layer was proposed and fabricated. By inserting the 50-nm-thick p-In0.01Ga0.99N layer, it was found that we could reduce the 20 mA forward voltage from 3.34 to 2.99 V. It was found the inserted p-InGaN layer could also reduce the efficiency droop from 36.7% to 23.8%.

Pulsed Growth Epitaxial Method of GaN-Based Light-Emitting Diodes on Patterned SiO 2 AlN/Sapphire Template

In this paper, we investigated GaN-based light-emitting diodes (LEDs) with embedded air voids grown by pulsed growth epitaxial (PGE) method. The void shape can be successfully controlled using the patterned SiO2 AlN/sapphire template and pulsed growth method. By embedding the air voids, we could enhance the 20-mA output power by >61.9%, compared with conventional LED. The improvements could be attributed to the enhanced light extraction efficiency utilizing air voids and improved internal quantum efficiency through PGE method.