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To: sbaker23 who wrote (227)	3/19/2000 7:32:00 AM
From: John Finley	Read Replies (1) of 565

sbaker23, Thanks for the heads up. There is a nice cartoon of Samsung's violet laser if you click on the thumbnail of your link. 'Course they're using a sapphire substrate <g>. As Will pointed out previously Nichia has been making GaN substrates for a while by growing a thick GaN layer on sapphire then removing the sapphire. To me that sounds expensive and production limited. I had a vendor trying to sell me chemical vapor deposited (CVD) diamond once and it was cost prohibitive. I don't know how Samsung or Sumitomo grow their GaN so I can't take a stab at relative cost. However, in general, it's better to grow crystalline (epitaxial) films on a substrate of itself (homoepitaxy) than a different material's crystal structure (heteroepitaxy). The only advantage that I can think of for using conductive SiC over conductive GaN substrates (if the prices are comparable) is if you need to remove a lot of heat from the device. I don't know enough about it to know if heat is a problem. So, in other words, I don't know how these GaN growth announcements impact the market for SiC for these applications. I would venture that there will be an impact, though. JF

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