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To: kinkblot who wrote (103)	12/7/1999 9:25:00 PM
From: John Finley	Read Replies (2) \| Respond to of 565

I don't know about GaN boules. I ought to check with my old substrate vendors to see if they're doing anything similar. Let's see there was Shinkosha or some such, Eschete BV or some such, Commercial Crystal Labs (yippee, I remember one!)..... Anyway, I've got a list somewhere. They probably have websites now. Y'know, I wonder if the copper oxide superconductor substrates have the right lattice constants and thermal expansion coefficients? We used to use sapphire, yttria stabilized zirconia (YSZ), strontium titanate (STO), lanthanum aluminate (LAO), and magnesium oxide. Sapphire is cheap, YSZ is reasonable also up to 4", STO I don't think grows very well, LAO 4" also, and MgO is a wonder substrate but it's hard to grow and polish (2" wafers were $1k). Somewhere I've got all their properties. I'll look around. I can't imagine polishing off a sapphire substrate. That can't be cost effective. I seem to remember Eschete(?) growing STO with a flame spray method or some such. Probably wouldn't work for things that need a high purity. Superconductors are nowhere near as picky about impurities as semiconductors. Anyway enough rambling. I'll look for GaN substrates. JF