Question

Why is PN junction called a diode?

Answer 1

A PN junction is called a diode because it allows electrical current to flow in only one direction, similar to a valve that only lets water flow in one direction. Here's a simple breakdown of why this happens:

1. PN Junction: This is formed when two types of semiconductor material, P-type and N-type, are placed together. The P-type has an excess of holes (positive charge carriers), and the N-type has an excess of electrons (negative charge carriers).
   

1. Formation of the Junction: When these two materials are joined, some of the electrons from the N-type region move into the P-type region and combine with the holes. This forms a depletion region at the junction, which prevents further movement of charge carriers.
   

1. Diode Behavior:
   

   - Forward Bias: When a positive voltage is applied to the P-type side and a negative voltage to the N-type side, the depletion region shrinks, allowing current to flow easily. This is called forward bias.
   - Reverse Bias: When the voltage is applied the other way around (positive on N-side and negative on P-side), the depletion region widens, blocking the flow of current. This is reverse bias.

Because of this one-way current flow property, the PN junction behaves like a diode. In fact, the word "diode" comes from "di-" meaning two, and "-ode" meaning path, which indicates that the device has two terminals and allows current to flow in one direction only.