Reliability Study of GaN-based Blue LEDs Employing Composite Transparent Conducting Oxide with P-type Conduction

The enhanced luminous efficacy of blue light-emitting diodes (LEDs) would improve the luminous efficacy of white LEDs for solid-state lighting. In a typical blue gallium nitride (GaN) LEDs structure, the planar transparent conducting oxide (TCO) thin film acts as transparent contact electrode (TCE), and helps extract photons with its high optical transmittance. However, conventional TCE thin film, such as indium tin oxide (ITO), has limited utilization in future optoelectronic devices because of the rising cost of indium, its toxicity, poor chemical stability, and n-type conduction property. Thus, the development of new, low cost, environmentally-friendly, and p-type conduction TCO materials will significantly benefit the production of high luminous efficacy blue GaN LEDs.This proposed research aims to verify the stability of blue GaN LEDs with high luminous efficacy for integration in white LEDs used in residences, offices, and general lighting applications. The proposed blue GaN LEDs will contain a novel feature: composite TCO thin film (cTCO film) acting as TCE. The cTCO film will be optimized in the thermal annealing process, possessing low contact resistivity, high optical transmittance, and high chemical stability. Then, reliability of the blue GaN LEDs utilizing the cTCO film will be investigated. The proposed research is an extension of our previous work and demonstrates the validity of the concept in practical applications.