Explain how the barrier voltage is developed in it

Barrier voltage of a diode: The barrier voltage is the amount of electromotive force required to start current through the p-n junction.

The depletion or barrier voltage of a p-n junction is a region depleted of charge carries. Thus as a dielectric medium situated between two blocks of law resistance material; It has a capacitance. The barrier voltage capacitance is designated CPn, and its value may be calculated from the usual equation for parallel plate capacitance.

Typically CPn is 40PF. The barrier voltage capacitance is normally considered the capacitance of a reverse biased p-n junction.