Why is a photodide operated in reverse bias mode? Fig. shown reverse bias current, under different illuminating intensities `I_(1)I_(2),I_(3)` and `I_(4)` for a given photodiode. Average the intensities `I_(1), I_(2),I_(3)` and `I_(4)` in decreasing order of wavelength.

Explanation

The photodiodes are use4d in reverse bias condition because the change in reverse current through the photodiode due to change in light flux or light intensity can be measured easily, as the reverse saturation current is directly proportional to the light flux or light intensity. But it is not so when photodiode is forward biased.
As the reverse saturation current through a photodiode increases with the increase in light intensity or light flux, so `I_(4)gtI_(3)gtI_(2)gtI_(1)`.