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Technology Stocks : Wolf speed
WOLF 20.62+3.5%Nov 26 3:59 PM EST
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To: mauser96 who wrote (1976)2/10/2000 12:15:00 PM
From: Guy Gordon  Read Replies (1) of 10713
 
Sorry, Lucius. That is incorrect.

The reason has to do with the geometry of the LED. The light does not pass through the substrate. So the transparency of SiC or Sapphire is irrelevant. The light is generated in the GaN layer, and exits laterally. (There is another laser structure in which the light exits vertically.)

The big advantage of SiC as a substrate for LEDs are that it's lattice spacing matches GaN better than Sapphire. This leads to better quality GaN layers. Additional, smaller advantages are the thermal and electrical conductivity of SiC. The electrical conductivity allows Cree to put one electrode on the bottom of the LED, where Sapphire LEDs have to put both electrodes on the top. This leads to a small advantage in manufacturability.

There is one more advantage of SiC that applies to lasers. That is cleavage. When making a laser, you need to create a mirror cavity. With Sapphire based GaN lasers this is done by dry etching. With SiC, this is done cheaper via cleavage.
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