Semiconductor physics

Why is the intrinsic Fermi level of silicon slightly offset from the exact center of the band gap?

  1. ABecause the band gap disappears as the temperature rises
  2. BBecause the effective densities of states (effective masses) of the conduction and valence bands differ
  3. CBecause silicon crystals always contain impurities
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Answer: B. Because the effective densities of states (effective masses) of the conduction and valence bands differ

In an intrinsic semiconductor, the Fermi level sits where the electron and hole densities are equal. Because the effective densities of states of the conduction and valence bands differ due to different effective masses, the intrinsic Fermi level shifts slightly from the center. In silicon the shift is only about 0.01 eV at room temperature, so it can be treated as nearly mid-gap.

  • A. The band gap does not disappear when temperature rises.
  • B. Correct. The difference in effective densities of states causes a small shift.
  • C. The intrinsic Fermi level is defined for the ideal case without impurities.
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More Semiconductor physics questions

  1. Which value is closest to the band gap of silicon (Si) at room temperature?
  2. Which statement is correct when phosphorus (P) is added to silicon as an impurity?
  3. What happens to the intrinsic carrier density when the temperature of an intrinsic semiconductor is raised?
  4. Which correctly compares electron and hole mobility in silicon?
  5. Where is the Fermi level located in an n-type semiconductor?