Semiconductor physics

[miraj]

hi,
i want to ask the following questions.

1. why the fermi level in Intrinsic semiconductor lies in the middle of the energy band gap?

2. why the fermi level shifts towrads the conduction band in N type semiconductors?

3. why the fermi level shifts towards the valance band in the P type semiconductors?

 

[nikhilele]

fermi levels shifts because of increase in number of minority charge carriers.

and for np = ne its in middle

 

[elmolla]

You can think of the Fermi level as the center of gravity of the amount of free charge particles. i.e.
If the Fermi level is in the middle, then there is a balance between the number of free charge particles in the valency band (holes) and the number of free charge particles in the conduction band (electrons).
When it tends to be more shifted towards the valency band then there are more free charge particles in the valency band (holes) than in the conduction band (electrons) and vice versa.

Hope that helped

 

[Gundam001]

Take a look in this article, I think this can explain your question...

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi.html