Explain why elemental semiconductors cannot be used to make visible $LEDs$.

(N/A) The band gap energy of elemental semiconductors, such as silicon $(Si)$ or germanium $(Ge)$, is relatively small. For silicon, the band gap is approximately $1.1 \text{ eV}$, and for germanium, it is about $0.67 \text{ eV}$.
Visible light corresponds to photon energies ranging from approximately $1.8 \text{ eV}$ to $3.1 \text{ eV}$.
Since the band gap of elemental semiconductors is too small, the energy released during electron-hole recombination is insufficient to produce photons in the visible spectrum. Instead, they emit radiation in the infrared region.
Therefore, compound semiconductors with larger band gaps are required to produce visible light $LEDs$.