Question

In a forward biased photo-diode with increase in incident light intensity, the diode current:
A) Increases
B) Remains constant
C) Decreases
D) None of the above.

Answer 1

Hint:The semiconductor diodes or p-n junctions in which charge carriers are generated by photons are called optoelectronic devices. A p-n junction consists of a p-type semiconductor on one side and n-type semiconductor at the other side of a single crystal of silicon or germanium. It is also known as semiconductor diode or junction diode.

Complete step by step answer:
A photo diode is a reverse biased p-n junction which is designed to respond to light absorption. The current in a photo diode is directly proportional to the intensity of light falling on its p-n junction.

When light falls on the p-n junction, the energy is imparted by the photons to the atoms in the junction. This will create more free electrons (more holes). These excess free electrons will increase the reverse current. As the intensity of incident light on the p-n junction increases, the reverse current also increases. In other words, as the intensity of incident light increases, the resistance of the device decreases.
The circuit connections for a photo diode are as shown in fig. In reverse bias, the current through the junction is due to minority charge carriers. When a p-n junction is subjected to light, having a photon of energy greater than the energy gap. The photon will excite an electron from the valence band to the conduction band and a electron-hole pair is generated. The electron-hole pair generated in the depletion layer will be separated by the junction potential difference and made to flow across the junction. As a result there is an increase in reverse saturation current.

From these observations we can say, in a forward biased photo-diode with increase in incident light intensity, the diode current will also increase.

$\therefore $ Correct option is (A).

Note:
-Photo diodes are used in camera light meters and clock radios.
-In the receivers for remote controls in televisions, music systems and DVD players.
-For the accurate measurement of light intensity in science and industry.