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Technology Stocks : White light from LED
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To: John Finley who wrote (104)12/8/1999 9:26:00 AM
From: kinkblot  Read Replies (1) of 565
 
J. Mater. Res., Vol. 14, No. 7, July 1999, pages 2716-2731

This is a paper on the topic of current interest:
InGaN/GaN/AlGaN-based laser diodes grown on epitaxially laterally overgrown GaN, by Shiji Nakamura.

He does do it by polishing. In his words:

After obtaining the 20-micron-thick ELOG substrate, the GaN growth was continued up to a thickness of 100 microns. After the 100-micron thick GaN growth, the sapphire substrate was removed by polishing in order to obtain a pure GaN substrate with a thickness of approximately 80 microns.

For comparison, he fabricates laser diodes on both 80 micron thick pure GaN substrates and ELOG on sapphire substrates of the same total thickness (70 microns sapphire + 10 microns ELOG). The only cleaving he does is within the GaN crystal to create a mirror facet for laser operation. This helps him achieve single mode emission without any interference effects, and output power at current of 200 mA of 90 mW, the highest value reported (at publication) for a III-V nitride-based laser diode under RT-CW operation. Lifetime is increased by about a factor of 4 for the devices built on the pure GaN substrate versus ELOG on sapphire, he believes due to the lower thermal resistivity of the substrate resulting from the higher thermal conductivity of GaN. He concludes his paper:

"The ultimate substrate for GaN growth is GaN."

WT
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