Working: In diode (any type of diode), an electric field ‘E’ exists across the junction from n-side to p-side, when light with energy hn greater than energy gap Eg. illuminates the junction. Then electron- **** pairs are generated due to absorption of photons, in or near the depletion region of the diode. Due to existing electric field, electrons and holes get separated. The free electrons are collected on n-side and holes are collected on p-side, giving rise to an emf.
Due to this generated emf, an electric current of μA order flows through the external resistance.
Detection of Optical Signals:
It is easier to observe the change in the current with change in the light intensity if a reverse bias is applied. Thus, photodiode can be used as a photodetector to detect optical signals.
