Semiconductor physics

Where in the band gap is the donor level created by phosphorus in silicon?

  1. AJust below the bottom of the conduction band (about 0.045 eV below)
  2. BJust above the top of the valence band
  3. CNear the middle of the band gap
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Answer: A. Just below the bottom of the conduction band (about 0.045 eV below)

The phosphorus donor level is very shallow, about 0.045 eV below the bottom of the conduction band. Even with room-temperature thermal energy (about 0.026 eV), almost all donors are ionized and supply electrons to the conduction band. Deep levels near mid-gap come from impurities such as gold.

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More Semiconductor physics questions

  1. Silicon contains both donors at 5×10¹⁶ cm⁻³ and acceptors at 2×10¹⁶ cm⁻³ (room temperature, all ionized). Which describes it correctly?
  2. Why does the carrier density of n-type silicon drop sharply when it is cooled to cryogenic temperatures?
  3. Which recombination process becomes significant at high carrier concentrations, where the released energy is given to another carrier instead of being emitted as light?
  4. What is the approximate resistivity of n-type silicon with an electron density of 1×10¹⁶ cm⁻³ and an electron mobility of 1000 cm²/V·s? (Ignore holes; elementary charge 1.6×10⁻¹⁹ C)
  5. What is the energy difference between the vacuum level and the bottom of the conduction band of a semiconductor called?