'12th semiconductors'

What is semiconductors? And it's types.

1. Semiconductor Topic :- solid state 12 th std Presented by Shubhangi V. Meshram ( M. Sc chemistry )

2. Contents Semiconductors Intrinsic semiconductors Extrinsic semiconductors Dopping N-type semiconductor P- type semiconductors

3. What is semiconductor ? A semiconductor is a material which has electrical conductivity between the conductor and insulator. The conductivity of a semiconductor increases with increasing temperature, behaviour opposite to metal. Example:-metalloids silicon (si) and geramanium (Ge) are semiconductors.

4. The valence band in semiconductors is completely filled with electrons and conduction band is empty. empty conduction band filled valence band small energy gap

5. The electons in conduction band are free to move. when electric potential is applied to a semiconductors, it conducts a small amount of electricity. The energy gap between the two bands is smaller than that in an insulator

6. Intrinsic semiconductors:- It is a pure semiconductors material which has a very low but finite electrical conductivity is called intrinsic semiconductors. it is free from impurities. it has equal no. negative carriers (electrons) and positive carriers (holes). impurities does not affect its electrical behaviour.

7. at higher temperatures , there are mobile electrons in the conduction band and more vacancies in the valence band than at lower temperature. therefore semiconductors are insulator at low temperature and conductors at high temperatures.

8. Extrinsic semiconductors and dopping:- Semiconductors formed after adding impurities are called extrinsic semiconductors. In extrinsic semiconductors without breaking the covalent bonds can increase the charge carriers. The conductivity of a semiconductor can be increased by dopping. A doped semiconductor having higher conductivity than pure intrinsic semiconductor is an extrinsic semiconductor.

9. Dopping:- The process of addition of minute quantity of impurities to a semiconductors to increase its conductivity is called dopping. The added impurity is known as dopant. There are two types of extrinsic semiconductors. n- type semiconductors p- type semiconductors

10. n- type semiconductors n-type of semiconductors contains increased number of electrons in the conduction band. An n-type of semiconductors is obtained by adding group 15 element to intrinsic semiconductor which belongs to group 14. for example doping of si with phosphorous. si has a crystal structure in which each si atom is linked tetrahedrally to four other si atoms.

11. 2) p-type semiconductors A p- type semiconductors is produced by dopping a pure semiconductors material (si and Ge) with an impurity group 13 elements. for example:- pure Si doped with Boron. the B atoms occupied normal position of some of the Si atoms in the lattice. Boron atom has only three valence electrons so therefore B atoms form bonds with three Si atoms only. A hole has tendency to accept electron from its close vicinity. the holes move in the opposite direction.

12. Thank you