stu@ndcheg.cheg.nd.edu (Stuart Harvey on ndcheg) (02/14/89)
I read an article in "Compressed Air" (a magazine of applied technology and industrial management published by Ingersoll-Rand Co.) about on 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? Stuart Harvey stu@ndcheg.cheg.nd.edu
buyno@voder.UUCP (Matthew Buynoski) (02/14/89)
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.