Question

A p-n photodiode is fabricated with a semiconductor having band gap of 3 $ev$, then

• A. It can detect $\lambda =500nm$
• B. It cannot detect $\lambda =300nm$
• C. It can detect $\lambda =240nm$
• D. It cannot detect $\lambda =400nm$

Answer 1

The correct option is C It can detect $\lambda =240nm$

$\frac{1242}{\lambda }>3\lambda <\frac{1242}{3}\lambda <414nm{\lambda }_{max}=414nm$
It can detect all $\lambda$ which are less than 414 $nm$.