JEE Main 2021 · 25 February · evening · Single correct · +4 / −1
For extrinsic semiconductors; when doping level is increased;
- (a) Fermi-level of both p-type and n-type semiconductors will go upward for T > T F K and downward for T < T F K, where T F is Fermi temperature.
- (b) Fermi-level of p-type semiconductor will go upward and Fermi-level of n-type semiconductors will go downward
- (c) Fermi-level of p and n-type semiconductors will not be affected.
- (d) Fermi-level of p-type semiconductors will go downward and Fermi-level of n-type semiconductor will go upward.
Answer and solution
Answer (d) Fermi-level of p-type semiconductors will go downward and Fermi-level of…
Solution
Physics sir · 4 steps
Fermi level follows the majority carriers: more holes pull it down, more electrons push it up.
- Intrinsic start. In a pure semiconductor the Fermi level sits near the middle of the band gap, because electrons and holes are equal in number.
- n-type doping. Donor atoms add electrons near the conduction band. More donors mean more electrons in the conduction band, so the Fermi level moves upward, towards the conduction band.
- p-type doping. Acceptor atoms create holes near the valence band. More acceptors mean more holes, so the Fermi level moves downward, towards the valence band.
- So. Raising the doping level lowers the Fermi level in p-type and raises it in n-type, which is option (d).
The idea to keep. The Fermi level always shifts towards the band holding the majority carriers. Heavier doping means a bigger shift: up to the conduction band for n-type, down to the valence band for p-type.
Answer from the NTA final answer key. Solution by PrepWiser.