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In article <628@ndcheg.cheg.nd.edu>, stu@ndcheg.cheg.nd.edu (Stuart Harvey on ndcheg) writes:
> I read an article in "Compressed Air" (a magazine of applied technology
....
> going work at MIT that is looking at using diamond and a semiconductor
> material.  The advantages of diamond semiconductors are that they can
> withstand harsh environments and are capable of much higher speeds and
> power levels that GaAs. As an example of being able to withstand a 
> harsh environment a Schottky diode performed acceptably and  700 C
> (the highest recorded temperature for a semiconductor).
> My question is does anyone know the level of developement of these 
> devices and where I might find more information about the current
> technology?

 Diamond semiconductors are useful at high temperatures due to the large
bandgap of diamond (ca. 5ev if memory serves). However, this also means that
they do not work very well at lower (e.g. room) temperatures. The current levels
of technology are mostly focused on deposition of thin-film diamond onto suitable substrates. This is currently very hard to do for single crystals of any
size, but a lot of people are growing so-called polycarbon films, which are
somewhat similar to  polysilicon films except made of carbon atoms. These films
are extremely hard and have shown evidence of diamond bonding. There is a lot
of argument about whether it is really diamond "through and through" or  a mix-
ture of graphite, diamond, and even some silicon carbide (most of the substratesbeing used are SiO2 or Si).
	As to sources, I think there has been some recent survey in J.Vac.Sci.and Tech., but it is foggy. IEEE Electron Devices Letters has had some brief reports (again if memory serves as I don't have the journals here with me). There
have also been some popular reports of diamond semiconductors and/or thin films
in some of the Semi Industry trade rags such as Semiconductor International.
Exactly which one I don't remember.
	More interesting, and probably more advanced, is the work on silicon-carbide on silicon for heterojunction bipolar transistors. SiC shares some of the
advantages of diamond (durable, wide (2 ev) bandgap) but is more technologicallyamenable. Even so, it is only at the stage of making demo. devices like single
transistors, and that with poor yields even in a lab.
	Be very careful of the speed claims on diamond semiconductors. Most of what limits semiconductors is not electron velocity, but the RC time constants
of charging and discharging the internal capacitances of the  devices, as well
as the technological constraints of how to make very (sub 0.1 micron) narrow 
base widths on the transistors.