Explain with the help of a circuit diagram the working of a photodiode. Write briefly, how it is used to detect the optical signals?
Working of photodiode Photodiode is an optoelectronics device in which current carriers are generated by photons through photo excitation, i.e. photo conduction by light. Its working is based on photo conduction from light.
A photodiode is a special type p-n junction diode made of photosensitive semiconductor material. In such a diode, a provision i.e. transparent window is made to allow the light of suitable frequency to fell on it.
Suppose, the wavelength is such that the energy of a photon, is sufficient to break a covalent bond in valence band. When such light fells on the junction, new electron-hole pairs are created. The number of charge carriers increases, the conductivity of p-n junction photodiode increases with the increase in intensity of light felling on it. Symbolically, a photodiode is shown in the figure.