Question
How does the energy gap in an intrinsic semiconductor vary when doped with a potential impurity?
Solution
The gap which is seperationg the valence band and the conduction band is known as fermi level.
When an intrinsic semiconductor is doped with impurity it becomes an extrinsic semiconductor.
Now, the fermi level will have to move away from it's mid-gap position inorder to conserve the number of particles as well as to maintain the electrical charge neutrality.
In an n-type semiconductor, energy gap decreases. Fermi-level shifts towards the conduction bandwhere, higher number of electrons are available for conduction. In a p-type semiconductor, energy band increases. Fermi levels shifts closer to the valence band because, holes are the majority carriers.
