N-type Semiconductor's Structure and Electric Conduction

We all know that the material which is semiconductor having two types which follows as
           [1] intrinsic semiconductor and
           [2] extrinsic semiconductor.

For the understanding of intrinsic type semiconductor please visit below post;
 

Post-3 How Silicon or Germanium is working as an Semiconductor ?

Now we come to the point and explain that what is the extrinsic donor semiconductor type; what is the meaning of 'N'; and what is the structure and its electric conduction.

First note that when we add any impurities in the intrinsic material then after these material becomes 'Extrinsic material' and the process of adding impurities is called "Doping".

Ex. Tetra-valent silicon will contain penta-valent impurities which are Phosphorus, Antimony and Arsenic.

The penta-valent element is the one which has five valence electrons and after add in the silicon base what effect is generated is shown in Fig.6a.
 

                                                            Fig.6a

When a penta-valent impurity such as Arsenic is added to the intrinsic semiconductor, four valence electrons of Arsenic atom construct four co-valent bonds with the four neighboring Silicon atoms as shown in Fig.6a.

The fifth electron of the Arsenic atom does not construct any co-valent bond with other and act as a free electron in the lattice-structure and take part in the electric conduction.

At the room temperature Si gets 0.01ev thermal energy and donate extra electron to the base silicon. that's why these type of impurities called "Donor impurities" Which indicated in Fig.6b.

                                                                            Fig.6b

The number of impurities electrons is one per 10^6 intrinsic atoms. It means that one mole lattice consists of 10^17 impurities electrons.

As a reason that A large number of free electrons are present along with a small number of thermally generated holes in an N-type semiconductor.

So the conduction largely takes place due to the free electrons. There fore the free electrons are called as "Majority Carriers" and holes are called as "Minority Carriers". 

                                                                   Fig.6c

Then after we talk about electric conduction, when an external DC voltage is applied to the N-type semiconductor material, the free electrons(called Majority charge carrier) move towards the positive terminal of the battery and holes(called Minority charge carrier) move towards to the negative terminal of the battery which indicated in Fig.6c.
 

For P-type semiconductor material wait to the next post.........

Post-7 P-type Semiconductor's Structure and Electric Conduction


 








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