Physics - Semiconductors Question with Solution | TestHub

For a photodiode to detect a signal, the energy of the incident photon must be greater than or equal to the band gap energy of the semiconductor.

$E\ge E_g$

$\frac{hc}{\lambda }\ge E_g$

$\lambda \le \frac{hc}{E_g}$

Substituting the given values:

$\lambda \le \frac{6.6\times 10^{-34}\times 3\times 10^8}{4\times 10^{-19}}$

$\lambda \le \frac{19.8\times 10^{-26}}{4\times 10^{-19}}$

$\lambda \le 4.95\times 10^{-7}\text{ m}$

$\lambda \le 4950\text{ A˚}$

Among the given options, only $4000\text{ A˚}$ is less than $4950\text{ A˚}$.

Answer: $4000$ Å