# For extrinsic semiconductors: when doping level is increased;

Question:

For extrinsic semiconductors: when doping level is increased;

1. Fermi-level of $p$ and $n$-type semiconductors will not be affected.

2. Fermi-level of p-type semiconductors will go downward and Fermi-level of n-type semiconductor will go upward.

3. Fermi-level of both p-type and n-type semiconductors will go upward for $T>T_{F} K$ and downward for $\mathrm{T}<\mathrm{T}_{\mathrm{F}} \mathrm{K}$, where $\mathrm{T}_{\mathrm{F}}$ is $\mathrm{Fermi}$ temperature.

4. Fermi-level of p-type semiconductor will go upward and Fermi-level of n-type semiconductors will go downward. }

Correct Option: , 2

Solution:

(2)

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.

$\&$ 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.