First slide

Opto electronic juction devices

Question

Statement I: A p-n junction with reverse bias can be used as a photo-diode to rneasure light intensity.
Statement II: In a reverse bias condition, the current is small but it is more sensitive to change in incident light intensity.

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

Photo-diode is a reverse biased p-n junction diode as shown in figure. At the p-r junction, there exists a junction field which at equilibrium, does not permit the flow of charge carriers across the junction.
When such a p-n diode is illuminated with light photons having energy hv> $E_{g}$ and intensities $I_{1}, I_{2}, I_{3}$ , etc., the electron and 6ole pairs generated in the depletion layer (or near the junction) will be separated by the junction field and made to flow across the junction. There would be a change in the reverse saturation current as shown in figure. Hence, a measurement of the change in the reverse saturation current on illumination can give the values of the light intensity.
Hence, option (1) is true.

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