Semiconductor physics

How does carrier mobility generally change when the impurity concentration in silicon is increased?

  1. AIt does not change
  2. BIt decreases
  3. CIt increases
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Answer: B. It decreases

At higher impurity concentrations, Coulomb scattering by ionized impurities (ionized impurity scattering) increases, so carrier mobility decreases. In heavily doped regions the resistivity is low, but the mobility itself is reduced.

  • A. Impurity concentration strongly affects mobility.
  • B. Correct. Ionized impurity scattering increases and mobility drops.
  • C. More impurities mean more scattering, so mobility does not increase.
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  3. Which value is closest to the electron mobility in lightly doped silicon at room temperature?
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