why we use impure semiconductors?

Semiconductor ?

You find semiconductors at the heart of microprocessor chips as well as transistors. Anything that's computerized or uses radio waves depends on semiconductors.

A semiconductor is a solid material that has electrical conductivity between those of a conductor and an insulator; it can vary over that wide range either permanently or dynamically. Most semiconductor chips and transistors are created with silicon

The property of semiconductors that makes them most useful for constructing electronic devices is that their conductivity may easily be modified by introducing impurities into their crystal lattice. The process of adding controlled impurities to a semiconductor is known as doping.

Intrinsic Semiconductor

Extrinsic Semiconductor

Doping Process

While making semiconductors, the electronic properties of semiconductor materials such as; silicon, Gallium Arsenide(GaAs), Germanium etc is altered by the semiconductor manufacturers. This process of altering which makes an element work as a semiconductor is called doping.

The process of doping consists of including or adding some atoms of external elements into an insulator such as silicon. In other words it is called bringing “impurities” into a pure element.

The material which is altered to develop semiconduction properties is called bulk while the added atoms are called the dopant.

Commonly, after the completion of the doping process, we get two types of semiconductors. These are n-type and p-type semicomductors. More clearly, these two types of semiconductors depend on the way we accomplish the doping process.

The doping process has got two types :

Doping for n-type semiconductors : It is advisable to choose a dopant which energy level is very much near to the conduction band of the insulator.

As there is no huge gap between the energy levels of the dopant and the insulator, the transferring of electrons from the dopant to the insulator or bulk requires very little amount of energy to lose in the process.

Along the process, the valence band is left with no corresponding holes and the process ends up creating negative electrons. Thus this concentration of negatively-charged-electrons-only give us n-type semiconductors.

Doping for p-type semiconductors : To make p-type semiconductors, a dopant with almost empty energy level, or with an energy level slightly better than the valence band of the insulator is used.

Thus it requires very little effort by the electrons present in the valence band to slide into the higher level of the dopant. This movement of electrons leaves open a number of positive holes in the valence band of the insulator. This process gives p-type semiconductors.

These two types of semiconductors are widely used in all types semiconductor products. For any semiconductor products manufacturer, it is impossible to think to produce a single chip or a transistor without semiconductors. Semiconductor material like silicon or germanium is used to make IC's( Integrated Circuits)