Question

For extrinsic semiconductors, when doping level is increased :

• A. Fermi-level of $P$ and $N$ - type semiconductors will not be affected.
• B. Fermi-level of $P$-type semiconductors will go downward while the Fermi-level of $N$-type semiconductors will go upward.
• C. Fermi level of both $P$-type and $N$-type semiconductors will go upward for $T$ > $T_f\text{K}$ and downward for $T$ <$T_f\text{K}$, where $T_f$ is the fermi temperature.
• D. Fermi - level of $P$-type semiconductor will go upward and Fermi - level of $N$-type semiconductors will go downward.

Answer 1

The correct option is B Fermi-level of $P$-type semiconductors will go downward while the Fermi-level of $N$-type semiconductors will go upward.

In $N$-type semiconductor , pentavalent impurity is added.
Each pentavalent impurity donates a free electron. So, the Fermi-level of $N$-type semiconductor will go upward.

However , in $P$-type semiconductor trivalent impurity is added. Each trivalent impurity creates a hole in the valence band. So, the Fermi-level of $P$-type semiconductor will go downward.