Continually improving white LEDs depends to a great extent on proprietary improvements in the chemistry and art of phosphor deposition. Cree considers that part of its intellectual property very secret. However, McClear was willing to talk about a recent breakthrough in backend processing, one that he figures the competition will catch onto fairly quickly. In fact, the development has to do with the LED diodes themselves.
In normal practice, when the diodes on a wafer are singulated, the surface over the junction is smooth—smooth as a mirror. And like a mirror, it tends to reflect some photons back into the chip, where they’re lost. Cree came up with a surface-roughening technique that eliminated the mirror effect, producing a 10% to 25% improvement in both brightness and lumens per watt. Little things make a difference.
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