The photodiode is used to detect the optical signals. These diodes are preferably operated in reverse biased mode because

A photodiode is used to detect optical signals and is preferably operated in reverse bias mode.

Why reverse bias?

In reverse bias, the current through the photodiode is primarily due to minority carriers. When light falls on the junction, it generates electron-hole pairs (minority carriers in their respective regions).

In reverse bias mode, the dark current (without light) is very small since it depends only on minority carriers. When light is incident, the photogenerated minority carriers cause a significant fractional change in the total current.

This fractional change in minority carriers produces a higher reverse bias current, making the photodiode more sensitive to optical signals in reverse bias mode.

In forward bias, the current is dominated by majority carriers, and the small photocurrent due to minority carriers would be negligible compared to the large forward current, making detection difficult.

The correct answer is Option D: fractional change in minority carriers produce higher reverse bias current.