Oxidation and diffusion

What is the correct unit of the diffusion coefficient D?

  1. Acm⁻³
  2. Bcm/s
  3. Ccm²/s
Show answer and explanation

Answer: C. cm²/s

The diffusion coefficient expresses how much area the spread covers per unit time, so its unit is cm²/s (or m²/s). The characteristic spreading distance is √(Dt); multiplying cm²/s by time in seconds and taking the square root gives a length.

  • A. cm⁻³ is a unit of concentration.
  • B. cm/s is a unit of velocity.
  • C. Correct. The diffusion coefficient has units of cm²/s.
Practice this topic Back to topic

More Oxidation and diffusion questions

  1. Which correctly expresses Fick's first law? (J: diffusion flux, D: diffusion coefficient, C: concentration, x: position)
  2. When diffusing impurities at the same temperature, if the diffusion time is quadrupled, by roughly what factor does the spreading distance change?
  3. In thermal diffusion, which pair correctly gives the profile shapes for diffusion with a constant surface concentration and for diffusion of a fixed amount of impurity?
  4. Which compound has been used as a liquid diffusion source for introducing phosphorus into silicon by thermal diffusion?
  5. Which set represents the commonly used classification of charges in and at the interface of the oxide in a MOS structure?