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PRACTICE / Energy bands

A band gap sets an absorption energy threshold

An ideal direct-gap semiconductor has a band gap of 2.0 eV. Use hc = 1240 eV·nm.

What is the longest vacuum wavelength whose photon energy can bridge this gap?

Organize the givens & assumptions
  • Eg = 2.0 eV
  • hc = 1240 eV·nm

Ideal interband absorption threshold, available final states, negligible excitonic, phonon and defect effects. Photon energy at least Eg is necessary in this simplified direct-gap model; absorption probability is not specified.

  1. A1240 nm1240\ \mathrm{nm}
  2. B310 nm310\ \mathrm{nm}
  3. C620 nm620\ \mathrm{nm}
  4. D2480 nm2480\ \mathrm{nm}

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