Question

Photo-diode is operated in reverse bias because

• A. When the diode is reversed biased, no ordinary current flows and the detection of the photo-current is much easier.
• B. When the diode is reversed biased, ordinary current flows and the detection of the photo-current is much easier.
• C. In reverse biased it will conduct a lot of current and can't detect the small amount of excess current produced by the photoelectric effect
• D. All of the above

Answer 1

The correct option is A When the diode is reversed biased, no ordinary current flows and the detection of the photo-current is much easier.

When a photo-diode is reverse biased, the width of depletion layer increases as compared to forward biased and a small reverse current (dark current) flows through the diode . Now , when the light is incident on the junction, electron-hole pairs are generated in depletion layer in a big amount (due to broad depletion layer) and these charge carriers can easily cross the barrier, hence contribute to current across the diod.

We can say that in reverse bias, diode changes the incident light to current , more effectively due to broad depletion layer i.e. when the diode is reversed biased , no ordinary current flows and the detection of the photo current is much easier.