Semiconductors

Substances which allows electricity to flow through them are called conductors. While materials that don't allow the flow of current are known as insulators. Some substances behaves as both conductor and insulator depending on some conditions, such materials are called semiconductors. 

Semiconductors are widely used in electronic industry e.g computer and communication. They have revolutionised the world of engineering and technology. They have a crystaline structure. Examples of Semiconductors are germanium and silicon. 

They are use for rectification, oscillation, RF generation etc. To cut it short they are the building blocks of  mordern electronics circuits and smart electronics. 

Mode of conduction of Semiconductors.

Semiconductors are different from pure metals because of their mode of conduction. Electricity is conducted in semiconductors by holes and free electrons. In an atom of germanium or silicon there are four valence electrons in the outermost orbit. In it purest form and absolute temperature  all electrons are bonded to their orbit and the crystal is not a conductor of electricity.But when it temperature is increased the electrons becomes mobile and therefore conducts electricity. 

 

Types of Semiconductors.

There are two types of Semiconductors, the N-type and the P-type semiconductor. The N-TYPE is produced by introducing of suitable foreing element into  a pure germanium or silicon and that process is called doping.

 Semiconductor in forward bias.

For example if we add an impurity like arsenic or antimony to a pure germanium crystal, the crystal structure is altered  and it produces much free electrons than holes(positive charge).  When a battery is connected to it as show above the free electrons moves towards the positive terminal of the battery and causes a current to flow in the circuit.  

P-TYPE semiconductor is made by doping a pure germanium or silicon crystal with an impurity such a boron or indium. The result produced more holes than free electrons. when connected to a battery holes moves from it to the negative terminal the battery. 

Holes are the majority charge carrier while electrons are the minority carrier.

P-N junction diode.

 

When an N-TYPE semiconductor is joined to a P-TYPE semiconductor it acts as a single crystal known as P-N junction diode, such an alloy with a very thin junction between the two semiconductors can be produced by a special industrial process. The P-N junction functions like a thermionic diode, it is use for rectification, and blocking current when connected in reverse bias. If we connected a battery to the diode as shown below  

P-N Junction diode in forward and reverse bias.

with the positive terminal of the battery connected to the P-type and the  negative terminal of the battery connected to the N-type current flow freely in the circuit, thus it conducts electricity and this is called the forward bias.  If the circuit is reversed that the battery's  negative terminal is connected to the P-type and the positive terminal is connected to the N-type semiconductor, there is no current flow and this is called the reverse bias. 

Thus for this property the diode is use for AC-DC rectification.

 

Appllications of Semiconductors.

 

1. They are use for manufacturing integrated circuits since they occupy a very little space. They are use for logic chips, computer and robots CPU and ALU chips. 
2. They are use for manufacturing diodes like LASERs,photocells,LEDs etc. 
3. They are use for manufacturing Transistors, high power MOSFETs and power oscillators etc. They are use for making microwave generator chips.