It is possible to manufacture a single piece of a semiconductor material half of which is doped by P-type impurity and the other half by N-type impurity.
The plane dividing the two zones is called junction. Theoretically, junction plane is assumed to lie where the density of donors and acceptors is equal. The P-N junction is fundamental to the operation of diodes, transistors and other solid-state devices.
Let us see if anything unusual happens at the junction. It is found that following three phenomena take place:
- A thin depletion layer or region (also called space-charge region or transition region) is established on both sides of the junction and is so called because it is depleted of free charge carriers. Its thickness is about 10-6 m/ 1-micrometer.
- A barrier / junction potential is developed across the junction.
- The presence of depletion layer gives rise to junction and diffusion capacitances
