Semiconductor Materials

 Semiconductor Materials

Semiconductor Materials

We are already know the conducting and insulating materials.

Conducting materials are good conductors of electricity. For examples - gold, copper, silver, aluminium, etc.

 

Insulating materials are bad conductors of electricity like glass, porcelain, quartz, rubber, Bakelite, etc.

 

Generally for electricity copper or aluminum are used in wires.  These wires provide an easy path for the flow of electric current.

The wire is covered with some insulating material such as rubber, PVC, plastic, etc. These covering provides protection against short circuits and also against electrical shock hazards.

 

There is another group of materials, such as germanium and silicon. These are neither good conductors nor good insulators.

At room temperature these materials are less conductive as compared to the conductive materials, but higher than insulator materials. Due to this behavior, these materials are classified as semiconductors.

The following table shows the resistivity of some commonly used conductors, semiconductors and insulators at room temperature:

Materials	Conductivity (S/m)	Resistivity Ωm	Classification
Silver	6.25 * 77	1.6*10-8	Conductors
Copper	5.88*107	1.7*10-8	Conductors
Aluminum	3.85*107	2.6*13-8	Conductors
Germanium	1.54	6.5*10-1	Semiconductors
Silicon	5.0*10-4	2.0*103	Semiconductors
Porcelain	3.33*10-10	3.0*109	Insulator
Glass	5.88*10-12	1.7*1011	Insulator
Hard Rubber	1.0*10-16	1.0*1016	Insulator

When we increase the temperature the conductivity of the conductor materials are decreases, but when we increase the temperature of the semiconductor materials the conductivity of semiconductors are increase.

 

In other words we say internal resistance of conductor is increase on high temperature.

And internal resistance of semiconductors is decrease on high temperature.

 

So we say that the semiconductors have negative temperature co-efficient of resistance.

 

The semiconductors have another very important property. The conductivity of a semiconductor can be changed to a very large extent, if we add a little amount of some specific materials (called impurities).

The conductivity of the semiconductor can also be controlled by controlling the amount of impurity added to it.