High-Power and High-Efficiency InGaN-Based Light Emitters

In this paper, we report on the latest advancements in improving AlGaInN-based visible-light-emitting-diode (LED) efficiency in epitaxy, chip, and package designs. We investigate the fundamental origin of the typical high current ?droop? of efficiency observed in such LEDs. We show that this effect is most likely not caused by incomplete carrier injection or carrier escape but that it is rather a fundamental material property of InGaN/GaN-heterostructure-based light emitters. The droop can be reduced in improved epitaxial LED active-layer designs. We show how this can be achieved by lowering InGaN volume carrier density in multiple quantum wells (MQWs) and thick InGaN layers. Improved epitaxial MQW structures are then combined with a new advanced chip concept. It is optimized for high efficiency at high current operation and arbitrary scalability and can be manufactured at low cost. This is accomplished by improving light-extraction efficiency, homogenizing the emission pattern, reducing forward voltage, and lowering thermal resistance. The improved high current efficiency can be fully exploited by mounting the chip in the highly versatile new OSLON SSL package. It features very stable package materials, a small footprint, and an electrically isolated design decoupling electrical and thermal contacts.     

Quality and thermal stability of thin InGaN films

Laser diodes with InGaN quantum wells emitting at long wavelengths are required for the application in compact laser projection. However, quantum wells with indium contents higher than 20% show weak photoluminescence performance as a result of high defect densities. We analyzed the root causes of the low performance of such quantum wells in detail. The influence of the indium content, the annealing temperature and the barrier structure on the quantum-well stability was investigated. We found that quantum wells with indium contents higher than 20% degrade due to the diffusion of indium atoms. Vertical diffusion coefficients for different barrier materials are extracted.