Question

A $p-n$ photodiode is made of a material with a band gap of $2.0eV$. 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 $=2eV$.
Wavelength of radiation corresponding to this energy,
$\lambda =\frac{hc}{E}=\frac{12400eV\mathring{A}}{2eV}=6200\mathring{A}$
The frequency of this radiation
$=\frac{c}{\lambda }=\frac{3\times 10^{8}m/s}{6200\times 10^{-10}m/s}$
$\Rightarrow v=5\times 10^{14}Hz$