Semiconductors are materials with controllable conductivity that is intermediate between conductors and insulators. They conduct electricity better than insulators but not as well as conductors. Semiconductors require less energy than insulators but more than good conductors to remove electrons for conductivity. Common semiconductor materials include silicon, germanium, and compounds like gallium phosphide. Semiconductors can be classified as intrinsic, containing a limited number of free electrons and holes, or extrinsic, which are doped with impurities to add more electrons or holes to increase conductivity.

1. SEMICONDUCTORS
Rakesh Huike (7744)
Eric Paul (7745)

2.  Semiconductor is a material with controllable conductivities ,
intermediate between conductors and insulators.
 They conduct electricity better than insulators but not as well as
conductors.
 As the elctrons are in bound state at low temperatures the
semiconductors behave like insulators at absolute zero
temperature and develop significant conductivities at room
temperature.

3.  Semiconductors require energy less than insulators and more than
good conductors to remove an electron from the parent atom for
conductivity.
 The semiconductor materials contain limited number of free electrons
that can act as a negative charge carriers.
In addition, the vacancies left behind when electrons leave their
normal positions act as carriers of positive charge . These vacancies
are called holes.

4. Semiconductor material mostly used are :
1. Silicon (most common)
2. Germanium
3. Selenium
4. Indium
5. Gallium
some oxides like:
1. Gallium phosphide
2. Aluminium phosphide

5. • Semiconductors have a regular crystalline structure
• Silicon has mainly a diamond structure

6. Conduction
Band
Valence
Band
Conductor Semiconductor Insulator
Overlap
Band
Gap
More Band
Gap
Energy gap

7. Semiconductor
Intrinsic extrinsic
p-type n-type
Semiconductor classification

8. • Intrinsic semiconductor
Intrinsic conductor is a conductor having conductivity caused due to ejection
of an electron from a covalent bond.
Ejected electrons leave holes (i.e vacancies) in the bond, both the electron
ejected and the vacancies contribute in conduction .
Intrinsic semiconductors are the pure type of semiconductors.
An intrinsic semiconductor has a filled valance band at about 0° k and
completely empty conduction band . As a result behaves like a insulator.

9. Electrons
• Conduction band
Energy Gap
• Valence band
Holes
Mechanism of conduction in intrinsic semiconductor at room temperature

11. Extrinsic semiconductor
 Extrinsic semiconductors are conductors which conduct due to excess or
conduction electron provided by an impurity added by DOPING .
 The impurities added provide an extra electron for conduction .
In extrinsic semiconductors there are 2 types ;
1. n-type extrinsic semiconductor
2. p-type extrinsic semiconductor

12. • N-type extrinsic semiconductor
N-type semiconductors are the pure intrinsic type of semiconductors
which are doped by foreign atom which donates it one valance
electron.
 The foreign atom acts as a donor in this case.

13. • P-type extrinsic semiconductor
p-type semiconductors are the semiconductors in which the foreign atom
provides an excess hole by accepting a valence electron from the intrinsic
type semiconductor.
The foreign atom is so called a acceptor in this case.

14. Transitors
Thermistors
APPLICATION OF SEMICONDUCTORS

15. CONCLUSION…..
• The semiconductors are totally temperature dependent .As
temperature decreases it looses its conductivity ( i.e behaves like a
insulator) and behaves like a conductor around the room
temperatures.
Needs to be operated nearly to room temperatures for good
conductivity more than the insulators.

16. REFERENCES….
Material Science And Technology……….By O.P. Khanna

17. Thank you..