Answer to Question #102621 in Classical Mechanics for BIVEK SAH

Question

How does the Fermi energy of n- and p- type semiconductors change with dopant
concentration

Answer 1

Fermi level shifts upward from its intrinsic value when the device is n-doped and shifts downwards when p-doped.

The concept is actually simple. When you n-dope a material, there are more electrons than holes and it is easy for the free electrons to gain very low energy and jump into conduction band. This idea is represented by the upward shift of Fermi level. Assume that all the electrons are sitting at the Fermi level (which is very close to conduction band now) and they can shift to conduction band by gaining a few eV of energy.

Similarly, when the device is p-doped holes can easily jump to valence band and this phenomenon is represented by shift of Fermi level near the valence band.