Semiconductor physics

Silicon contains both donors at 5×10¹⁶ cm⁻³ and acceptors at 2×10¹⁶ cm⁻³ (room temperature, all ionized). Which describes it correctly?

  1. Ap-type, with a hole concentration of about 2×10¹⁶ cm⁻³
  2. Bn-type, with an electron concentration of about 3×10¹⁶ cm⁻³
  3. Cn-type, with an electron concentration of about 7×10¹⁶ cm⁻³
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Answer: B. n-type, with an electron concentration of about 3×10¹⁶ cm⁻³

When both donors and acceptors are present, they cancel each other out (compensation). Donors outnumber acceptors, so the material is n-type, and the electron concentration is the difference: 5×10¹⁶ − 2×10¹⁶ = 3×10¹⁶ cm⁻³. The conductivity type and concentration of a source or drain formed by implantation inside a well are determined the same way.

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More Semiconductor physics questions

  1. Why does the carrier density of n-type silicon drop sharply when it is cooled to cryogenic temperatures?
  2. Which recombination process becomes significant at high carrier concentrations, where the released energy is given to another carrier instead of being emitted as light?
  3. 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)
  4. What is the energy difference between the vacuum level and the bottom of the conduction band of a semiconductor called?
  5. In lightly doped silicon, what is the main reason mobility decreases as temperature rises?