Low single charge carrier density materials?

  • Thread starter uby
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  • #1
uby
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Main Question or Discussion Point

Hello all,

I am trying to identify materials having a single dominant charge carrier having extremely low (on the order of 10^15 cm^-3) concentrations. Metals and extrinsically doped semiconductors, while both possessing a single dominant charge carrier (electrons or holes), tend to have carrier densities on the order of 10^23 cm^-3, which is about 8 orders of magnitude greater than I desire.

[Intrinsic semiconductors are unsuited for my application, since the concentration of electrons and holes are by definition equal (I need a single charge carrier to be dominant). Polymers are probably unsuited for my application as well, which will be above 400C.]

Are there any resources out there with data compilations for charge carrier densities at elevated temperatures?

Also, if there isn't any material that possesses such a low charge carrier density, is it possible to modify the band structure by application of a bias voltage or some other external means?

Thanks,
--uby
 

Answers and Replies

  • #2
uart
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10^15 cm^-3 is no problems at all for Si. The intrinsic concentration for Si is about 10^10 cm^-3 at 300k so 10^15 (either p or n) is pretty much a mid range doping level. Levels lower than this are commonly used in higher voltage Si devices.
 
  • #3
uby
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10^15 cm^-3 is no problems at all for Si. The intrinsic concentration for Si is about 10^10 cm^-3 at 300k so 10^15 (either p or n) is pretty much a mid range doping level. Levels lower than this are commonly used in higher voltage Si devices.
Thanks uart, I was unaware of this. My application will probably be around 700K or so, and I'm unsure what the intrinic concentration becomes at such an elevated temperature, but I will direct some effort into finding some Si data.

Do you happen to know of any resources that speak towards the theory of intrinsic charge carrier densities for semiconductors (especially oxides)?
 
  • #4
uart
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Thanks uart, I was unaware of this. My application will probably be around 700K or so, and I'm unsure what the intrinic concentration becomes at such an elevated temperature, but I will direct some effort into finding some Si data.

Do you happen to know of any resources that speak towards the theory of intrinsic charge carrier densities for semiconductors (especially oxides)?
Yeah the intrinsic concentration is a very strong function of temperature. I've got a graph here that indicates around 10^16 for Si at 700k, so it looks like you'd need to use a wider band-gap material. I don't know a great deal about the properties of semiconductors other than Si so maybe someone else might chime in with some good suggestions. I know that there are definitely other semiconductors available with wider band-gap, but I don't know much about their commercial availability.
 
  • #5
uart
Science Advisor
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Looking at the following table, semiconductors with a band gap of around 2 eV or more would probably be suitable for your application (Ni much less than 10^15 cm^-3 @ 700k).

http://en.wikipedia.org/wiki/Band_gap
 
Last edited:
  • #6
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This is why SiC and Diamond are seen as natural high temperature semiconductors.

Cree has commercialize the former fairly well. I don't know of anyone who's tackled diamond yet commercially.
 

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