Question

A $p-n$ photodiode is made of a material with a band gap of $2.0 \,eV$. The minimum frequency of the radiation that can be absorbed by the material is nearly

• A. $1 \times 10^{14}\, Hz$
• B. $20 \times 10^{14}\, Hz$
• C. $10 \times 10^{14}\, Hz$
• D. $5 \times 10^{14}\, Hz$

Answer 1

Answer: (D)

Band gap $=2 eV$.
Wavelength of radiation corresponding to this energy,
$\lambda=\frac{h c}{E}=\frac{12400 eV \,\mathring{A} }{2 eV }=6200 \,\mathring{A} $
The frequency of this radiation
$=\frac{c}{\lambda}=\frac{3 \times 10^{8} \,m / s }{6200 \times 10^{-10}\, m / s } $
$\Rightarrow v=5 \times 10^{14} \,Hz$