Plenary Talks
High power LEDs for solid state lighting
Dr. Berthold Hahn
Osram Opto Semiconductors
For solid stated lighting high light output in combination with high conversion efficacy is essential. High efficiencies are relatively easy to realize at low current densities, but efficiency tends to decline as the current is cranked up. In order to overcome the barriers for high flux LEDs, both epitaxy and chip design have to be optimized.
In this paper we report on the improvement of ThinGaN®-PowerLED structures in epitaxy, chip design, phosphor efficiency and package design. A key for improving LED performance is understanding the carrier loss mechanisms in blue and green epitaxy structures. Assuming an indirect Auger effect as one of the major loss mechanisms in InGaN LEDs, a reduction of the carrier density per emitting well is enabling efficiency improvement for blue/green LEDs.
Along with improved epi designs the extraction efficiency had to be improved. A new chip designs allows high current operation in combination with efficiencies beyond 100lm/W for white. New conversion schemes allow the fabrication of extremely efficient green light sources, which enable new generations of high flux projection applications.
Another key parameter is reliability. The degradation mechanisms of epi, phosphor and package had to be analyzed and optimized in order to ensure lifetimes beyond 50.000h.