DIAMOND ELECTRONICS
Single-crystal CVD diamond exhibits the highest carrier mobilities at room temperature of any wide-bandgap semiconductor, has the highest thermal conductivtiy of all known materials and has an exceptionally high breakdown voltage.
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If various technical challenges can be overcome, diamond would be particularly well suited to operation as a semiconductor material wherever high frequencies, high powers, high temperatures or high voltages are required.
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CVD DIAMOND
Diamond has always been an outstanding and desirable material. With the invention of synthetic growth techniques at high pressures and temperatures in the fifties, it became technical material, especially for mechanical applications. However, it was the advent of low pressure deposition techniques that made accessible the excellent mechanical, thermal, optical and electronic properties. With these chemical vapour deposition (CVD) techniques diamond became available in the form of extended thin films and free-standing plates or windows. Doping during deposition could be realized, making diamond a p-type semiconductor. With CVD-diamond a wealth of new applications opened up.
The fundamental problem of diamond synthesis is the allotropic nature of carbon. Under ordinary conditions graphite, not diamond, is the thermodynamically stable crystalline phase of carbon. Hence, the main requirement of diamond CVD is to deposit carbon and simultaneously suppress the formation of graphitic sp2-bonds. This can be realized by establishing high concentrations of non-diamond carbon etchants such as atomic hydrogen. Usually, those conditions are achieved by admixing large amounts of hydrogen to the process gas and by activating the gas either thermally or by a plasma.
Hence, a common feature of all diamond CVD techniques is a gas-phase nonequilibrium, i.e. a high supersaturation of atomic hydrogen and of various hydrocarbon radicals. Typical deposition conditions are: 1 % methane in hydrogen as source gas, 700-1000°C deposition temperature and gas pressures in the range 30-300 Torr.