Question

Whatv is the reason to operate photodiodes in reverse bias?

Answer 1

A photo diode operates in the reverse bias mode. When the light is incident on the junction surface,electron-holes pair are created. This is because valence electrons are liberated after absorbing radiant energy. As electron hole pair increases,reverse electrical current increases,i.e increase in electron hole pair is directly proportional to the number of photons striking the junction surface. Therefore as the intensity of light increases, saturation current also increases. Because its not much use in the forward bias direction, it will conduct pretty much like a normal diode. The magic happens in the reverse bias condition where the reverse current (in a normal diode you might call it leakage current) is dependent upon and proportional to the amount of light power hitting the junction. There is also a component called dark current which is the tiny leakage current which flows when there is no light. The current can be readily converted to a voltage using a transimpedance amplifier. Hope it helps