Discussion
The band gap of a material is Eg and the energy of an incident photon is Ep. Optical absorption will occur in this material if,
Answer: A
Optical absorption occurs when \(E_{g} \lt E_{p}\).
A photon is absorbed across the band gap by lifting an electron from the valence band into the conduction band, leaving a hole behind. That is possible only if the photon carries at least the band gap energy, so the photon energy must exceed (or at least equal) Eg. This is why a semiconductor is transparent to light with photon energy below its gap.
If \(E_{g} \gt E_{p}\) the photon cannot bridge the gap and passes through. Electron-hole recombination is the reverse process, which emits light (as in an LED) rather than absorbing it, and 'electron-electron recombination' is not a physical process.
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