Semiconductor physics

What type of band structure does silicon have?

  1. ADirect band gap
  2. BIndirect band gap
  3. CMetallic, with no band gap
Show answer and explanation

Answer: B. Indirect band gap

Silicon is an indirect-gap semiconductor: the conduction-band minimum and valence-band maximum sit at different positions in momentum (wave-vector) space. For an electron and hole to recombine and emit light, a phonon (lattice vibration) must take part to supply the momentum, so light emission is very inefficient. LEDs and lasers therefore use direct-gap materials such as GaAs, InP and GaN. Absorption, however, can occur with phonon assistance, so silicon works well as a photodetector.

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More Semiconductor physics questions

  1. What can be learned from a Hall effect measurement?
  2. What is a semiconductor called whose impurity concentration is so high that the Fermi level lies inside the conduction or valence band?
  3. Which is the Einstein relation between the diffusion coefficient D and the mobility μ of carriers? (k: Boltzmann constant, T: absolute temperature, q: elementary charge)
  4. Which value is closest to the thermal voltage kT/q at room temperature (300 K)?
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