Question:
If a semiconductor photodiode can detect a photon with a maximum wavelength of $400 \mathrm{~nm}$, then its band gap energy is :
Planck's constant, $h=6.63 \times 10^{-34} \mathrm{~J} . \mathrm{s}$.
Speed of light, $\quad c=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$
Correct Option: , 4
Solution:
(4)
Given,
Wavelength of photon, $\lambda=400 \mathrm{~nm}$
A photodiode can detect a wavelength corresponding to the energy of band gap. If the signal is having wavelength greater than this value, photodiode cannot detect it.
$\therefore$ Band gap $E_{g}=\frac{h c}{\lambda}=\frac{1237.5}{400}=3.09 \mathrm{eV}$
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