Getting a grip on sapphire etching: Novel clamping of sapphire looks to unleash brighter, cheaper LEDs
By Dr Mark Dineen, Oxford Instruments
[Originally published in Compound Semiconductor January/February 2015 edition]
MANUFACTURERS OF LEDs are striving to make cheaper devices that emit more light. If they succeed, sales will rise, and these chipmakers will enable the LED to increase its deployment in an ever-growing number of applications.
One common and effective route for increasing the bangperbuck of the LED is to switch the foundation for the device from a flat sapphire substrate to one that has been etched to form a patterned surface. This alternative, known as patterned sapphire, is increasing in popularity because it delivers two key benefits to the makers of high-brightness LEDs:
It increases the fraction of light emitted from the device, thanks to the controlled texture
It leads to a lower density of defects within the film, thanks to growth on a three-dimensional landscape that spurs earlier coalescence of GaN epitaxial islands during MOCVD growth
The downside of turning to patterned sapphire is that etching this material into useful patterns is not easy. There is a processing cost involved, and this must be low enough to not negate the benefit associated with increased LED performance.
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