Energy band Diagrams

What is conduction band and Valence band?

These bands define the specific amount of energy present in given shell of electrons.Valence bands specify the energy level of electrons in valence shell of atomic structure whereas conduction band specifies the energy of electrons in conduction band and are responsible for conduction.Valence and conduction bands are separated by certain amount of energy level which is known as energy gap.Energy gap plays an important role for all the mechanisms of energy band diagrams.

  

                The upper,lower and yellow boxes represent the conduction band, valence band and occupancy level of electrons respectively

Energy band Diagrams for metals,semiconductors, Insulators

Above Diagram depicts the following Features:

a & b)Metals consisting of one or two valence electrons

c)Semiconductor in which band is close enough with valence band

d)Insulator having larger energy gap

 Let's come down to our topic of interest :

Semiconductor energy band diagram

• Intrinsic

Following are the keypoints to note in Intrinsic Semiconductor:

1)In Intrinsic semiconductors the Fermi energy level is halfway between the valence

and conduction bands.

2)Here we are considering the band diagrams at absolute

zero temperature hence there is no conduction.

3) At higher temperatures a finite number of electrons can reach the conduction band

and provide some current.

• Extrinsic

In case of Extrinsic Semiconductors, addition of p-type and n-type semiconductors

changes the fermi energy level

1)Adding N-type impurity increases the electron density in the conduction band and

in turn it becomes easier for electrons to excite to conduction band, hence the

fermi energy level increases.It shifts towards conduction band.

2)The exact opposite happens when P-type impurity is added i.e as the electron

density of conduction band decreases , it requires more energy to excite the electrons

to the conduction band. Hence the Fermi Energy level shifts towards the valence band.

The shift depends on the extent of doping of impurity.

Source/Image Courtesy:

1)https://eng.libretexts.org/Bookshelves/Materials_Science/Supplemental_Modules_

(Materials_Science)/Semiconductors/Fermi_level#Energy_Band_Diagram

Author : Ruturaj Deshmukh