For extrinsic semiconductors; when doping level is increased;

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 semiconductor will go upward and Fermi-level of n-type semiconductors will go downward.
  3. Fermi-level of both p-type and n-type semiconductors will go upward for T>TF K and downward for T<TF K, where TF is Fermi temperature.
  4. Fermi-level of p- type semiconductors will go downward and Fermi-level of n- type semiconductor will go upward.

Solution

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.

Asked in: MHT CET Full Test 12

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