Question

For detecting the light______.
A. The photodiode has to be forward-biased
B. The photodiode has to be reversed biased
C. The LED has got to connected in forwarding bias mode
D. The LED has got to be connected in reverse bias mode

Answer 1

In reverse biasing of a PV junction diode the width of the depletion region becomes thick. The increased width of the depletion region offers lesser resistance and more current flows in reverse biasing. A photodiode is used to detect light.

Complete step by step answer:
Working of Photodiode:
The working rule of a photodiode is, when a photon of ample energy strikes the diode, it makes some of an electron-hole. This mechanism is also known as the inner photoelectric effect. If the absorption arises within the depletion region junction, then the carriers are removed from the junction by the inbuilt electric field of the depletion region.

Therefore, holes within the region move toward the anode, and electrons move toward the cathode, and a photocurrent will be generated. The photodiode operates in the mode of photoconductive. When the diode is connected in reverse bias, then the depletion layer width can be increased. So, this will diminish the capacitance of the junction and the response time. This biasing will cause quicker response times for the diode. So, the relation between photocurrent and illuminance is linearly proportional.

In reverse biased conditions, the width of the depletion region increases as the applied reverse bias voltage increases across the diode. So, by applying a bigger voltage, more of the incident photons are converted to current thereby increasing the efficiency.

In forward biased conditions, the width of the depletion region decreases so only a little portion of the incident photons get converted to current, and hence the efficiency is a smaller amount.

Hence, the correct answer is option (B).

Note: The current in a pn junction diode always flows in a single direction.
Then the negative side of the battery is connected to the p side of the diode this is called reverse biased.
The photodiode only works in reverse biasing because the depletion region is thick and offers lesser resistance in reverse biasing hence a little amount of photon can generate a considerable amount of energy.