Semiconductor physics

What happens to the drift velocity of electrons in silicon when a strong electric field is applied?

  1. AIt keeps increasing in proportion to the field
  2. BIt approaches a certain value (about 1×10⁷ cm/s) and hardly increases further
  3. CIt decreases as the field becomes stronger
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Answer: B. It approaches a certain value (about 1×10⁷ cm/s) and hardly increases further

At low fields the drift velocity is proportional to the field, but at high fields scattering in which carriers lose energy to lattice vibrations increases, and the velocity levels off at about 1×10⁷ cm/s. This is called velocity saturation and limits the current of short-channel MOSFETs.

  • A. The velocity is proportional to the field only at low fields.
  • B. Correct. Velocity saturation occurs at high fields.
  • C. A velocity drop at high fields occurs in some materials such as GaAs; in silicon the velocity saturates.
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More Semiconductor physics questions

  1. Which value is closest to the energy of a single photon of light with a wavelength of 620 nm? (E [eV] ≈ 1240 / λ [nm])
  2. How does carrier mobility generally change when the impurity concentration in silicon is increased?
  3. Which is the correct definition of the work function of a material?
  4. Which value is closest to the relative permittivity of silicon?
  5. Which value is closest to the electron mobility in lightly doped silicon at room temperature?