Sang Hern Lee

Enhanced Optical Output Power of Tunnel Junction GaN-Based Light Emitting Diodes with Transparent Conducting Al and Ga-Codoped ZnO Thin Films

High quality Al and Ga-codoped ZnO (AGZO) thin films were successfully deposited both on sapphire substrates and GaN-based light emitting diodes (LED) with a tunnel junction (TJ) layer by using the radio frequency magnetron sputtering technique at room temperature. The AGZO thin films grown on sapphire substrate showed high transparency (96.3% at 460 nm) and low resistivity (6.8 ×10-4 Ω cm). The AGZO thin films deposited on the GaN-based LED with a TJ layer exhibited weak ohmic behavior although it improved slightly with the annealing. The optical output power of the TJ GaN-based LED with an AGZO transparent conducting layer was about 12.6 mW at 20 mA, and the external quantum efficiency was 23.0%. These values are approximately 1.7 times larger than that of the TJ GaN-based LED with a conventional Ni/Au layer.

Light Extraction of High-Efficient Light-Emitting Diodes

This chapter deals with methods for fabricating high-efficient light-emitting diodes (LEDs) with higher light extraction efficiency (LEE). Some LED prototypes are then reviewed to investigate how their performance was enhanced by utilizing a variety of chip processes. The most efficient devices were found to be produced with unique fabrication processes, having at least one patterned sapphire substrate, chip shaping, vertical configuration, and/or flip-chip packaging, among others.

Light Extraction Efficiency Part B. Light Extraction of High Efficient LEDs

This chapter deals with methods for fabricating high efficient light-emitting diodes (LEDs) with higher light extraction efficiency (LEE). Some LED prototypes are then reviewed to investigate how their performance was enhanced by utilizing a variety of chip processes. The most efficient devices were found to be produced with unique fabrication processes, having at least one patterned sapphire substrate, chip shaping, vertical configuration, and/or flip-chip packaging, among others.

High performance of GaN-based flip-chip light-emitting diodes with hole-shape patterned ITO ohmic contact layer and AgIn reflector.

The enhancement of light extraction efficiency is observed when the hole-shape patterned ITO ohmic contact layer and AgIn reflector is adopted in GaN-based flip-chip (FC) light emitting diodes (LEDs). ITO layer (140 nm) and AgIn (200 nm) was deposited on the top of p-GaN by in-line DC sputtering and electron beam evaporating system, respectively. The ITO ohmic contact layer showed a low specific contact resistance of 2.66 x 10(-5) Omega cm(-2) and high transmittance of >85% at visible spectral regions. The AgIn reflector exhibited a low specific contact resistance of 1.90 x 10(-5) Omega cm(-2) and high reflectance of approximately 84% at visible spectral regions. Comparing with unpatterned ITO/AgIn layer, the optical output power of GaN-based FC LEDs improves approximately 30% by the adoption of micro size hole-shape patterned ITO ohmic contact layer and AgIn reflector.