Zero biased junction diode

A diode is said to be ZERO BIASED when it is connected in a circuit -- for instance, with its two terminals simply shorted together -- but with no external potential energy applied to the junction from any source. Even under these conditions, some HOLES on the p-side (the majority carriers there) have enough thermal energy on their own to overcome the potential barrier and cross into the n-side; the small current this produces is called the FORWARD current. Symmetrically, a few thermally generated MINORITY carriers on the n-side (holes generated there by thermal bond-breaking) also drift across the junction in the opposite direction, producing what is called the REVERSE current. This continual, spontaneous back-and-forth transfer of carriers across the junction is exactly the diffusion process described earlier.

The potential barrier at the junction prevents any FURTHER net diffusion of MAJORITY carriers beyond this point, but minority carriers -- the small number of free electrons naturally present in the p-region and holes naturally present in the n-region -- continue to drift across regardless. An EQUILIBRIUM is reached once the majority-carrier crossings in each direction become equal in number, moving in opposite directions, so that the net current flowing across the junction as a whole is exactly zero; this state, in which microscopic crossings never actually stop even though the macroscopic net current is zero, is called a state of DYNAMIC EQUILIBRIUM. …