How do semiconductors emit light?

How do semiconductors emit light?

• A. By absorbing photons
• B. By releasing electrons
• C. By going to the outer shells of their atoms
• D. By recombining holes and electrons

Answer: (C)

Light emission in semiconductors comes from radiative recombination of electrons in the conduction band with holes in the valence band. In a crystal, electrons occupy energy bands rather than discrete atomic shells. When an electron from the conduction band recombines with a hole in the valence band, the released energy exits as a photon. The photon’s energy closely matches the material’s bandgap, which is why the color of the light is determined by the bandgap value. This mechanism is different from transitions to outer atomic shells in isolated atoms; in a solid, the relevant transitions are between energy bands (or through impurity/defect levels), not individual atomic orbitals. Direct-bandgap materials enable efficient light emission because momentum conservation is straightforward, whereas indirect-bandgap materials require phonons and emit light less efficiently.

Light emission in semiconductors comes from radiative recombination of electrons in the conduction band with holes in the valence band. In a crystal, electrons occupy energy bands rather than discrete atomic shells. When an electron from the conduction band recombines with a hole in the valence band, the released energy exits as a photon. The photon’s energy closely matches the material’s bandgap, which is why the color of the light is determined by the bandgap value. This mechanism is different from transitions to outer atomic shells in isolated atoms; in a solid, the relevant transitions are between energy bands (or through impurity/defect levels), not individual atomic orbitals. Direct-bandgap materials enable efficient light emission because momentum conservation is straightforward, whereas indirect-bandgap materials require phonons and emit light less efficiently.