06 Dec 2002
Sumitomo Electric and Procomp have formed a joint venture to produce zinc-selenide white LEDs.
Sumitomo Electric has teamed up with Procomp to commercialize zinc-selenide (ZnSe) white LEDs. The companies plan to establish a joint venture under the name Supra Opto Inc, with Procomp holding 60% ownership and Sumitomo the remainder. Mass production is expected to begin in March 2003, with a production volume of 1 million units per month, rising to 3.6 million units/month by the end of next year.
Sumitomo will transfer technology and equipment to Procomp, which will carry out epitaxial growth through its Procomp Informatics epiwafer division and chip processing through its Suntek foundry subsidiary.
Sumitomo developed ZnSe-based white LEDs about four years ago. The company's device is a homoepitaxial ZnSe blue LED grown on a ZnSe substrate, which simultaneously produces blue light from the active region and yellow emission from the substrate.
This differs radically from conventional white LEDs, which are made by combining a blue LED chip with a yellow phosphor, or a UV LED with a tricolor or polychromatic phosphor. Sumitomo's approach should avoid the patents owned by Nichia, Osram and others in this field.
Sumitomo says that the ZnSe LED offers a number of advantages. In conventional white LEDs, the use of a phosphor makes packaging more complicated and reduces the overall efficiency of the device. The ZnSe substrate is conducting, allowing the use of top and bottom contacts, unlike GaN-on-sapphire devices. Also, the ZnSe LED operates at a low voltage of 2.7 V, and is highly resistant to static electrical discharge.
Furthermore, the ZnSe LED offers an extensive range of color temperatures (3500 - 8500K compared to 6000 - 8500K for most GaN-based devices). This should allow the devices to provide warm-color lighting favored by American and European households.
Tim Whitaker is editor of Compound Semiconductor magazine.
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