IV.18 - Exotic-Semiconductor (SiC, etc) Diodes?

Here's a link to the NASA Lewis Research Center SiC (silicon carbide) page. Silicon carbide is just great for high temperature applications - up to 600 C, anyways. Silicon only goes up to 350 C, at the very most. This chart, borrowed from this NASA page and credited to Phil Neudeck, shows the clear promise of SiC - despite the lower mobilities, SiC ultimately has a higher saturation velocity than Si, so high-field devices will operate faster. Also the breakdown electric field and the energy gap are both higher, which is desirable for high-voltage and high-temperature operation, respectively. Plus the thermal conductivity is much higher than silicon's, making heat-sinking much easier. On the down side, the small wafer diameter are indicative of the difficulties in obtaining high quality SiC crystals - a major problem that must be overcome before commercialization can occur.

Click here for info on III-V compound-semiconductor devices and research, and here for the unofficial II-VI semiconductor home page.

Here's some nice intro material on Mercury cadmium telluride (HgCdTe) photodiodes.

This link takes you to the GaAs PIN Power Diode section of this FAQ.

Here's what Fred Olschner, 72142.365@compuserve.com, told me about the availability of other wide bandgap diodes:

• you asked if there are wide bandgap diodes available. Yes, there are some, however most wide bandgap semiconductors cannot be made to have non-linear I-V curves due to a large number of energy states within their large bandgaps. This makes the creation of a depletion region difficult. Even when very high purity crystal growth is attempted (e.g. thallium bromide, lead iodide, which have greater than 2 eV bandgap), only linear I-V are obtained. This is because the large number of energy states cause tunneling breakdown, which create effectively ohmic contacts.

  Although wide bandgap semiconductors can usually only have ohmic contacts, they still can exhibit low leakage currents, as their resistivities can be very high: 10^12 ohm-cm for mercuric iodide and lead iodide.

  These materials are generally used for room temperature solid state X-ray detectors, because their low leakage currents can reduce the electronic noise to low levels.

  Semiconductors having bandgaps in the range 1.3 to 1.7 eV might be made with some non-linear I-V curves, however it is generally a hard problem to get the energy state density low enough. CdTe, for example, using some special contact materials can be made to have diode-like properties (p-i-n). Other more developed semiconductors like InP and GaAs can also be made pure enough to produce good diodes.