Semiconductor devices - Barrier potential
N-type and P-type materials are considered electrically neutral before they are joined at a junction common. However, after the junction diffusion takes place instantaneously, when the electrons pass through the junction to fill the holes causing the emergence of negative ions in the material P, this action causes the area near the junction to take a charge. negative. The electrons leaving the material N cause it to generate positive ions.
This whole process, in turn, causes the N side of the junction to take a net positive charge. This particular charge creation tends to push electrons and remaining holes away from the junction. This action makes it somewhat difficult for other charge carriers to diffuse across the junction. As a result, charge accumulates or a barrier potential emerges across the junction.
Likeshown in the following figure. The resulting barrier potential has a small battery connected across the P-N junction. In the given figure, observe the polarity of this potential barrier with respect to the P and N materials. This voltage or potential will exist when the crystal is not connected to an external energy source.
The barrier potential of germanium is approximately 0.3 V and that of silicon is 0.7 V. These values cannot be measured directly and appear through the charge region space of the junction. In order to produce current conduction, the barrier potential of a P-N junction must be overcome by an external voltage source.