4. ELECTRICAL CONDUCTIVITY
Conductivity defines a material’s ability to conduct
electricity.
Electric current can flow easily through a material
with high conductivity.
In order of conductivity: Conductor, semiconductor,
insulator are comes.
6. CONDUCTOR
valence band only partially
filled.
next allowed empty band
overlaps with it.
All the atoms jumps to
conduction band.
Examples copper, iron.
7. INSULATOR
Energy gap is very wide.
Energy gap in Insulator is
more than 9 eV
electricity can’t conduct
Examples wood, plastic
8. SEMICONDUCTOR
It Lies between insulators and
conductors are called
Semiconductor .
Examples Si, Ge
Energy gap is very small.
They are of two types :
1. INTRINSIC
2. EXTRINSIC
9. DOPING
A semiconductor , which is in its extremely pure form , is known
as Intrinsic semiconductor.
Germanium and Silicon are most widely used semiconductor.
Silicon crystal contribute 4 valence electron.
The atoms are bounded by covalent bond.
10. INTRINSIC SEMICONDUCTOR
These are undoped
semiconductor.
It has equal number of
electrons and holes.
These are also called pure
semiconductors.
Ex.=Si, Ga.
11. EXTRINSIC SEMICONDUCTOR
These are doped semiconductors.
It has not equal number of electrons and holes.
This semiconductor obtained by doping of trivalent and
pentavalent impurities in a tetravalent semiconductor.
These are also known as impure semiconductors.
12. Extrinsic Semiconductor
Two types of impurity atoms are added to the
semiconductor
Atoms containing 5
valance electrons
(Pentavalent impurity
atoms)
e.g. P,As,Sb,Bi
Atoms containing 3
valance electrons
(Trivalent impurity atoms)
e.g. Al,Ga,B,In
N-type semiconductor P-type semiconductor
13. N-TYPE MATERIAL
Donor (n-type) impurities:
dopant with 5 valence electrons (e.g. P, As, Sb)
four electrons used for covalent bonds with surrounding Si
atoms, one electron “left over”
left over electron needed only small amount of energy to lift it
into conduction band (0.05ev in Si)
“N-type semiconductor”, has conduction electrons, no holes.
14. P-TYPE MATERIAL
Acceptor (p-type) impurities:
dopant with 3 valence electrons (e.g. B, Al, Ga, In)
only 3 of the 4 covalent bonds filled
vacancy in the fourth covalent bond hole.
“p-type semiconductor”, has mobile holes, very few mobile
electrons.