Semiconductor

Now science and technology are so advanced and world is diminished by it .Day by day new technology is invented. In semiconductor field , there are so advanced and new.S/C(semiconductor) is neither conductor nor insulator.It is depend upon the temperature.There are
many semiconductor devices like diode, transistors,IC(integrated circuit).Without semiconductor all electronics equipments was not invented and world not so developed.
These are solids in which the forbidden energy gap between the valence band and conduction band is small,of the order of 1eV.At zero kelven temperature,the valence band is completely filled and conduction band is completely empty .At 0K ,it behaves as an isulator (electron can not absorb infinite small energy because there is forbidden gap just above the top of the valance bands .At finite temperature ,some electron gain energy due to thermal motion and jumpe from the top of the valance bands to the conduction band .These electron contribute to the conductions of electricity in the S/C.
The forbiden gap in S/C is small 1eV.At finite temperature ,some valance electron goes to conduction band.Then the formlessly is in the middle of the gap . The energy gap in some S/C is as followings:
silicon=1.12eV
Germinium=0.7eV
Indium antimonide=0.7eV
Gallium arsenide=1.43eV
Tellurim=0.33eV
The energy gap decercase slightly with the increase the temperature.
Type fo Semiconductors

1. Intrinsic S/C
2. Extrinsic S/C

Intrinsic S/C is a pure form of S/C.The impurity must be les than 0.01 parts per millon . At low temperature all the valance electron are tightly bonded and no free electron is aviable for electrical conduction .So this type of S/C behaves as a prefect insulator at zero kelven temperature .If the temperature is increase then ,some of the electron may gain enough thermal energy and move away from the influnce of th nucleus i.e the covalent bond may be broken and it act as conductor.

There are two type of Extrinsic semiconductor ,one is P-type semiconductor and other is N-type semiconductor .Co valence element like Silicon(Si),Germanium (Ge)etc are used to made those two type of s/c.The proces of adding impurities to the S/C element is called doping.Mostly those two type of element is used mostly.If pentavalent element(from group V such as Arsinic ,antimony, phosphrous etc.) is doped in Silicon or Germanium in proper quantity then this type of semiconductor is known as N-type semiconductor where as if trivalent element(from III group such as Aluminium,Gallium,Indium etc.) is doped in proper quantity then this type of semiconductor is known as P-type semiconductor.The conductivity of extrinsic S/C is controlled by the amount of doping .In N-type semiconductor ,majority carrier is electron and minority carrier is hole where as in P-type of semiconductor,majority carrier is hole and minority carrier is electron.