Semiconductor physics

What is a semiconductor called whose impurity concentration is so high that the Fermi level lies inside the conduction or valence band?

  1. AIntrinsic semiconductor
  2. BInsulator
  3. CDegenerate semiconductor
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Answer: C. Degenerate semiconductor

When the impurity concentration becomes very high, the Fermi level moves outside the band gap (into the conduction or valence band) and the material behaves almost like a metal. This is called a degenerate semiconductor. Heavily doped regions such as sources, drains and tunnel diodes fall into this category.

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