Question
What limits the number of electrons available for conduction in an n-type semiconductor at room temperature?
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Electrical conduction occurs in most circumstances by the transport of electrons or holes or both, although there are exceptions. When a potential is applied (ie, in an electric field) electrons travel towards the positive pole and holes to the negative.
Exceptions
Current can also be carried by ions or any charged particle if these are mobile.
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The nature of the majority carrier depends on the band structure of the conductor. Only electrons or holes which can increase their energy slightly can contribute to conduction. In practice, this means electrons near the Fermi level in a metal or carriers close to the band edges in a semiconductor.
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