Junction Diode

It conducts an electric current in one direction and blocks it in the reverse direction. This property comes from the electrical characteristics of a junction, called a p-n junction made up within a semiconductor crystal. The most commonly used semiconductor materials are silicon or germanium. The p-n junction is also the major part of other electronic devices, of which the most well-known is the junction transistor.

PN Junction Basics

P=Holes or defiency of electrons

N=Available Electrons

Near Junction electrons diffuse with holes making a depletion region. N Type doping is done by arsenic, phosphorus and P type, Boron.

Forward Biasing : Shrinking of Depletion Layer, & A large diffusion current is able to flow.

Reverse Biasing: Depletion Layer Grows and very small reverse current flows.

The junction diode is useful in a wide range of applications such as

•  Rectification of AC signals

•  Detection of radio signals

• Conversion of solar power to electricity

• Used in electronics circuits like switch, as a voltage reference
  
  The rejoining of free electrons makes a narrow region on either side of the junction that contains no mobile charge. This narrow region which has been depleted of mobile charge is called the depletion layer. This layer extends into both the p-type and n-type regions. There is then a separation of charges: negative fixed charges on the p-type side of the depletion layer and positive fixed charges on the n-type side.

Junction Breakdown

It occurs when the reverse voltage reaches a critical value.