Page 3 - Lesson Note 5
P. 3
3. Semiconductors:
-6
-1
4
-1
Conductivities in the range 10 to 10 ohm m
Band theory of metals:
Atomic orbitals of metal atoms overlap to form a large number
ofmolecular orbitals very close in energy. This set of molecular orbitals
is called a band.
The band formed by the lower energy valence orbitals is called valence
band and the band formed by higher energy valence orbitals is called
conduction band. On applying electric current, electrons can flow from
valence band to conduction band.
Explanation of behavior of conductors, insulators and semiconductors
on the basis of band theory:
(1)Conductors:
In case of conductors, the valence band is partially filled or it overlaps
with conduction band then electrons can easily flow by the electric
field.
(2)Insulators:
In case of insulators, the gap between valence band and conduction
band is large and electrons can’t jump from valence band to conduction
band. This large energy gap is called forbidden zone.
(3)Semiconductors:
