Electronics - Doping

DOPING
Points : Definition, Hole, Flow of Hole, p - n Junction, Formation, Forward Biased, Reverse Biased

Definition
Process by which the electrical conductivity of elements such as Silicon or Germanium is increased by adding in them a small amount of an element which has either three or five electrons in its atom is called doping.

Hole:
In p — type substances when tetravalent substance is doped with a trivalent element an unoccupied space developed due to the shortage of an electron and is known as a hole. This hole behaves like a positive charge.

Flow of Hole:
Due to the application of electric field electrons move towards hole and leave a positive charge or hole at the initial place of electron. Thus hole flow in opposite direction to that of an electron.

p - n Junction:
It is an electronic device. A p-n junction is formed by placing a p —type (Indium) on a plate of n-type germanium.

Formation:
Indium on heating melts and diffuses through a small part of the n — type germanium and converts this part of germanium into p — type. Thus a junction is formed between a p — type section and an n — type section of germanium. A brass base is used to fix the p — n junction. Leads arc attached to it and the crystal is sealed in a metal or glass container.

Forward Biased:
When a semiconductor diode is connected to a D.C. Source in such a way that p-side is connected to the positive terminal and n-side to the negative terminal and holes move from the p type to the n type and electrons move from the n — type to the p — type material across the junction it is called forward biased. It has very low electrical resistance.

Reverse Biased:
When a semiconductor diode is connected to a D.C. Source in such a way that P-side is connected to the negative terminal & n-side to the positive terminal and holes and electrons move away from the junction it is called reverse biased. Reverse biased diode develops very high resistance.