Breakthrough in the luminous efficacy of AIGaInP LED: tiny light sources with brilliant power
Regensburg, Germany. Osram Opto Semiconductors has made a breakthrough in the luminous
efficacy of AIGaInP LED. With the aid of thin-film technology, Osram has managed to more
than double the efficiency of these tiny light sources.
Ultra-bright light-emitting diodes based on the quartenary material combination AlGaInP/GaAs cover half the visible spectrum, ranging from yellowish-green to red. Since its first developments in 1992, this technology has been undergoing continuous improvements to increase the efficiency of the LED.
Progress in epitaxial technology and process engineering has been coupled with innovative chip design and packaging to raise the luminous efficacy of these devices. In late 2000, Osram Opto Semiconductors developed a new class of surface-structured LED reaching luminous efficacies of 25-30 lm/W in orange and red. However, in common with all the previous models, these surface-structured LED are also hampered by their very design. Although the light is internally produced with a high degree of efficiency, a large proportion is absorbed by the GaAs substrate used in these LED as the germinal nucleus for crystal growth.
Engineers at Osram have now turned to highly advanced thin-film technology to solve this problem. The so-called "substrate-less" LED still use the GaAs substrate for crystal growth, but afterwards they function without the base material, which effectively becomes ballast. With this new technology the upper side of the LED is coated with a metal layer after the epitaxy process, after which it is bound onto a new, thin carrier. The original GaAs substrate can then be removed, leaving behind just the thin, light-generating layer. The intermediate metal film is partially alloyed, allowing the alloyed part to act as an electrical contact and the non-alloyed part as a highly-reflective mirror. This technique allows far more light to be emitted than conventional LED designs. Red LED (615nm) can achieve a luminous efficacy of more than 50 lm/W.
Right from the beginning, the bonding process used to attach the original epitaxy disc to the new carrier was designed for 4" wafers. This results in a much higher yield of chips per wafer, and therefore lends itself to cost efficient mass production of LED. Walter Wegleiter, the project manager for the new LED, explains: "We believe that our new substrate-less AlGaInP LED are just the beginning of an exciting development of highly-efficient and ultra-bright LED. This innovative generation of LED will open up the door to a wide variety of new applications."
Contact: Markus Rademacher Tel: +49 89-62 13 25 97 Fax: +49 89-62 13 34 57 M.Rademacher@Osram.de
Markus RademacherTel: +49 89-62 13 25 97
Fax: +49 89-62 13 34 57
M.Rademacher@Osram.de
E-mail: M.Rademacher@Osram.de
