Question

Why is a pn junction called as a diode?

Answer 1

A PN junction is called a diode because it has the basic properties of a diode, which is a device that allows current to flow in only one direction.

Let’s break it down:

1. PN Junction: This is formed when a P-type semiconductor (which has more "holes" or positive charge carriers) is joined with an N-type semiconductor (which has more electrons, or negative charge carriers). At the junction of these two materials, an electric field forms, and this is called the depletion region.
   

1. Diode: A diode is essentially a two-terminal device that permits current to flow easily in one direction (forward bias) and restricts it in the opposite direction (reverse bias). When a PN junction is used in a circuit, it behaves exactly like a diode, meaning:
   

   - Forward Bias: If the P-type side is connected to the positive terminal of the power supply, and the N-type side to the negative terminal, the junction becomes conductive, and current flows easily through it.
   
   - Reverse Bias: If the P-type side is connected to the negative terminal, and the N-type side to the positive terminal, the electric field at the junction widens, and current doesn't flow (or it only flows in tiny amounts due to leakage).

So, when you make a PN junction, it has the characteristic of a diode because it allows current to flow in only one direction. This is why a PN junction is often called a diode in its simplest form!