Capacitance of p-n Junction

A capacitor has two parallel conducting plates (electrodes) separated by a dielectric (insulator). The insulator stores electric charge in the form of electric field. The electrodes of the capacitor allow electric current to flow in to them but the dielectric does not allow electric current to flow through it, though it efficiently allows electric field. The capacitance is directly proportional to the area of electrodes and inversely proportional to the distance between them. Similarly a reverse biased p-n junction diode stores electric charge in depletion region. The depletion region has immobile +ve and – ve carriers. In a reverse biased p-n junction, the p-type and n-type regions have low resistance and these act like the electrodes of the capacitor. The depletion region of the p-n junction diode has high resistance and it acts like the insulator. Thus, the p-n junction can be considered as a parallel plate capacitor. In depletion region, the elect...