With what considerations in view, a photodiode is fabricated? State it’s working with the help of a suitable diagram.

Even though the current in the forward bias is known to be more than in the reverse bias, yet the photodiode works in reverse bias. What is the reason? 

A photodiode is used to observe the variation in current when the light intensity changes under reverse bias condition below the breakdown voltage.

A material of band gap ~1.5 eV or lower is chosen so that solar conversion efficiency is better. Hence, Ga-As or Si material is chosen for the fabrication of photo-diode.

Working: It is a p – n junction fabricated with a transparent window to allow light photons to fall on it. Upon absorption, these photons generate electron hole pairs. If the junction is reverse biased using an electrical circuit, these electron hole pair move in opposite directions so as to produce current in the circuit. This current is very small and is detected by the micro-ammeter connected to the circuit. 

The change in reverse saturation current is directly proportional to the change in incident light intensity when photo-diode is operated in reverse condition. This is not the case when the photo-diode is forward biased.