Question

A p-n photodiode is fabricted from a semiconductor with a band gap of 2.5eV. It can detect a signal of wavelength

• A. 6000
• B. 4000
• C. 4000 nm
• D. 6000 nm

Answer 1

Answer: (B)

4000

We know that $E=\frac{hc}{{\lambda }_{max}}$

$\Rightarrow {\lambda }_{max}=\frac{hc}{E}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{2.5\times 1.6\times {10}^{-19}}=5000A$

The wavelength of signal must be less than ${\lambda }_{max}$

$\Rightarrow \lambda =4000$

Therefore the correct option is $B$