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

Higher doping increases Coulomb scattering by ionized impurities, so mobility drops. For electrons in silicon it falls from about 1350 cm²/V·s at 10¹⁵ cm⁻³ to roughly 100 cm²/V·s at 10¹⁹ cm⁻³, so resistivity falls less than the doping rises. This is one reason MOSFET channels should be lightly doped, and FinFETs and GAA devices can use undoped channels.

  • 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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More Semiconductor physics questions

  1. Which is the correct definition of the work function of a material?
  2. Which value is closest to the relative permittivity of silicon?
  3. Which value is closest to the electron mobility in lightly doped silicon at room temperature?
  4. In an indirect-gap semiconductor such as silicon, why is the probability of electron-hole recombination with light emission low?
  5. In a semiconductor driven out of thermal equilibrium by illumination or current injection, what are the levels introduced to describe the electron and hole densities separately?