First slide

Opto electronic juction devices

Question

Statement I: A P-N photodiode is made from a semiconductor for which band gap $E_{g}$ - 2.8 eV. This photodiode will not detect the wavelength of 6000 nm.
Statement II: A PN photodiode detect wavelength $λ$ if energy of incident light, i.e., $\frac{hc}{λ} > E_{g} .$ (Bandgap of semiconductor from which photodiode in made)

Moderate

A

Both statements I and II are correct.
B

Statement I is correct but statement II is incorrect
C

Statement I is incorrect but statement II is correct
D

Both statements I and II are incorrect.

Solution

For detection of a particular wavelength ( $λ$ ) by a PN photodiode, energy of incident light > $E_{g} \Rightarrow \frac{hc}{E_{g}} > λ$
For $E_{g} = 28 eV, \frac{hc}{E_{g}} = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{2.8 \times 1.6 \times 10^{- 19}} = 441.9 nm$
$i . e ., \frac{hc}{E_{g}} < 6000 nm, so diode will not detect the wavelength of 6000 nm .$

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