Question

Photo-diode is operated in reverse bias because
\[A)\]When the diode is reverse biased, no ordinary current flows and the detection of the photo-current is much easier.
\[B)\]When the diode is reverse 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

Hint: A photodiode is a diode which converts light incident on it to electric current. This diode is generally connected in reverse biased condition. We must know that in reverse biased condition, if we increase the reverse bias voltage, the depletion layer at the p-n junction will increase its thickness. If we need to detect photo-current we must have minimum ordinary current.

Complete answer: We shall know what a photo-diode is before moving on to the solution. A photo-diode is a semiconductor device by which we can convert light waves into electrical current.

Now, we will see why a photodiode is connected in reverse biased condition. Generally, if a diode is reverse biased, the width of the depletion layer increases and the current flow due to majority charge carriers will be minimal. Now, whenever light is incident on this reverse biased photo-diode, electron-hole pair gets generated in the depletion layer in large amounts because of the large width of the depletion layer and these charge carriers will easily cross the barrier.

So, we can conclude the statement as, a photo-diode is reverse biased because no ordinary current flows while reverse biased and the detection of photo-current is much easier. So, option a is the correct answer.
So, the correct answer is “Option A”.

Note:
The working mechanism of photo-diode is also known as inner photoelectric effect because, when a photon of required energy is incident on a diode, it makes an electron hole pair. These holes will move towards the anode and electrons will move towards the cathode. This flow of charges is creating photo current. The diode is generally connected in reverse bias condition because the thickness of depletion layer is directly proportional to photo current.