Question

Answer in brief.

Why should a photodiode be operated in reverse biased mode?

Answer 1

A photodiode operates in reverse bias because, as a photodetector or photosensor, it must conduct only when radiation strikes it. The dark current for zero illumination is negligibly small in the reverse biassed mode, on the order of a few picoamperes to nanoamperes. When illuminated, however, the photocurrent increases by several orders of magnitude.