Physics - Semiconductors Question with Solution | TestHub

The semiconductor used for fabrication of visible LEDs must have a band gap of at least $1.8\text{ eV}$.

Gallium Arsenide Phosphide (${\text{GaAs}}_{1-x}{\text{P}}_x$) is used for making LEDs of different colours such as red, yellow, and orange.

For example, ${\text{GaAs}}_{0.6}{\text{P}}_{0.4}$ ($E_g\approx 1.9\text{ eV}$) is used for red LEDs.

Gallium Arsenide ($\text{GaAs}$) has a band gap of $\approx 1.4\text{ eV}$ and is used for infrared LEDs.

Gallium Phosphide ($\text{GaP}$) is typically used for green LEDs.

Thus, $\text{Ga}-\text{As}-\text{P}$ is the material that emits red and yellow light.

Answer: $\text{Ga}-\text{As}-\text{P}$