Solid State Physics

Claude Bile

Science Advisor
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Hello all, I have a few problems that I am struggling with at the moment. I think I am missing a few notes, so it may be that I'm missing an equation or something.

1. What is the difference between extrinsic and intrinsic behaviour in a semiconductor? How can you determine what temperature a semiconductor material such as Silicon will revert to intrinsic behaviour, given the donor, intrinsic carrier concentration and the energy gap?

- I am thinking that intrinsic/extrinsic behaviour is related to the Fermi level and the donor and acceptor concentrations at a temperature, T. Intrinsic behaviour has the Fermi level close to midway between the valence and conduction bands, with nearly equal concentrations of donor and acceptor ions. Extrinsic behaviour has the Fermi level close to the conduction band (or valence band). I am looking for confirmation as to whether this is correct, and if not, where I am going wrong.

- I do not have an equation that gives a direct answer to this question. The best I have managed is gaining approximate expressions for the chemical potential for both intrinsic and extrinsic behaviour and showing at which temperature they are both valid. My main difficulty is that we are only given the intrinsic carrier concentration at room temperature and are not told how it varies with temperature. Is there an equation that gives this also, with only the information given above as stated in the 1st paragraph?

I apologise the long winded description of the problem, I thank anyone how takes the time to read this, whether you could answer my questions or not.
 

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