industry LED manufacturing
Inserting microstructures within the epilayers of a nitride LED can boost dispersion and ultimately increase chip efficacy, says Optogan’s Lauri Knuuttila and Pekka Törmä.
Coaxing more and more light out of high-brightness LEDs
operating in this sector, and every one of them is working really hard to keep its customers, while welcome new ones currently being served by rival firms.
T
One way to stand out from the crowd and win business is to offer superior technology. Several years ago, cutting- edge crystal quality with dislocation densities on the order of 1 x 107
cm-2 would have given a company a major head
start over its competitors. But many chipmakers can now boast of material quality as good as this, along with high internal efficiencies. So today, arguably the best way for a company to differentiate itself from the competition is to manufacture LEDs delivering unprecedentedly high extraction efficiencies.
At Optogan – a European chipmaker with production facilities for LED assembly in St. Petersburg, Russia, and high-volume chip production in Landshut, Germany – this is our key objective.
Getting light out of the LED chip is not easy, given the huge difference in the refractive indices of air and GaN. However, efficient light extraction is essential for the realisation of LEDs with state-of-the-art efficacy. This requires excellent device architectures that get very close to delivering their theoretical level of light extraction.
Numerous different approaches have been used by the industry to get more light out of the chip, and by far the biggest challenge is to build an LED that can successfully combine a handful of these approaches to yield a cutting- edge, cost effective chip.
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www.compoundsemiconductor.net June 2011
Our epimaxx LEDs that we have developed for lighting applications have been built with this goal. One of their hallmarks is that they are free from packaging because this simplifies light extraction, thanks to a reduction in the number of interfaces associated with the luminaire. Chip design is focused on maximising radiation from the top surface while minimizing radiation from back and sidewalls.
Several of the approaches that we have considered to boost the light extraction of a basic LED chip are highlighted in Figure 1. These desirable features have to be incorporated into the device during its fabrication, either during chip processing or the epitaxial growth of the nitride film. It is worth noting, however, that chip processing can have its downsides. It can lead to absorption in contact layers and defective areas, stifling
he LED chipmaking industry is incredibly competitive. There are many, many companies
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