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Other than increased energy handling capabilities, one of the main advantages of using wide band-gap semiconductors like SiC or GaN in power electronics applications is that the switching frequency can be increased. I've read this is due to wide band-gap semiconductors having higher electron mobility [reference].

But why is that? Is it a direct result of the wider band gap?

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    \$\begingroup\$ I guess that the WBG facilitates the high mobility in a way. Anything in the conduction band will be far away energetically from the bound states, so the interactions/scattering with the lattice will be much attenuated when compared to a low band gap material at the same temperature. \$\endgroup\$
    – tobalt
    Jul 5, 2023 at 18:46
  • \$\begingroup\$ I've read that this is due to wide band-gap semiconductors having higher electron mobility Where did you read it? Please put a link to the article. \$\endgroup\$ Jul 5, 2023 at 20:10
  • \$\begingroup\$ Here is the article where I read that information. "Wide bandgap materials tend to possess higher electron mobility and electron saturation velocity, allowing for switching frequencies up to 10 times higher than silicon." Edited original question to show this. \$\endgroup\$ Jul 5, 2023 at 20:36

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Is it a direct result of the wider band-gap?

No. Higher electron mobility is not a direct result of a wider band gap. Because not all wide band-gap (WBG) devices have higher electron mobility than Si (as can be seen from the table below).

So we can't say that the electron mobility and the band gap are related to each other. All we can say is "WBG devices tend to have higher mobility".

...the switching frequency can be increased

Yes, wide band-gap devices (SiC and GaN) can operate at higher frequencies than silicon (Si) devices can. But electron mobility is not the only related thing:

  • WBG devices have inherently lower parasitic capacitances, making switching at higher speeds possible.
  • SiC devices have better thermal conductivity (interestingly, GaN devices have almost the same thermal conductivity as Si, due to the crystal structure). This makes higher switching speeds and higher power densities possible with especially SiC devices. You can find papers on this topic such as this one or this one from Microsemi that I took the table below from:

enter image description here

  • WBG devices have higher saturation velocity which is basically the maximum speed that the electrons can reach under the presence of an electric field. Higher electron saturation velocity means faster electron transport, and therefore operation at higher frequencies.

  • and many more.

Please note that many of the factors above are not a direct result of a wider band gap. Two of the most apparent direct results of a wider band gap are

  1. Higher breakdown voltage
  2. Higher maximum allowable junction temperature e.g. 150°C for Si vs 700°C for SiC but note that carrier mobility is significantly affected by the temperature.

And I'm leaving the discussion on how (or can?) these two affect the maximum operation frequency to you and others.

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