What is a photo-diode?
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.
The common, traditional solar cell used to generate electric solar power is a large area photodiode. Photodiodes are similar to regular semiconductor diodes except that are exposed (to detect UV or X-rays or visual light to reach the sensitive part of the device so that the electron excitation can take place from valence band to the conduction band, thereby developing required potential difference.
How photo-diodes are operated?
A photo-diode is designed to operate in reverse bias When photo diode is directly biased it acts like normal diode. But in reverse biased mode current through the diode depends on the brightness and you can use this relation between brightness and current for something you want your circuit to do.
Why photo-diodes are preferably used in reverse bias mode?
A photo diode is a diode and it do act as a barrier in reverse bias as in the case of diode, but in case of photo-diode as the light falls on the reverse biased PN junction there forms a discharge that discharge leads to formation of new electrons and holes, as we have electrons and holes in the reverse bias PN junction and due to the external voltage applied across a the diode leads to the reverse break down (i.e Zenner breakdown)and hence the (minority dimonated) current flows. The number of electrons and holes in reverse bias junction depends upon the discharge which in turn depends upon the light intensity and with the increase intensity of light the current through the diode in reverse biase increases. Thus in reverse biased mode current through the diode depends on the brightness and you can use this relation between brightness and current for something you want your circuit to do.
In reverse biased mode the width of the depletion layer increases thereby reduces the junction capacitance and hence causes the faster response times for the photodiode. The photocurrent is linearly proportional to the illuminance.
In reverse biased mode the width of the depletion layer increases thereby reduces the junction capacitance and hence causes the faster response times for the photodiode. The photocurrent is linearly proportional to the illuminance.
