CBSE Class 12-science Answered

When a pentavalent impurity atom is added to a pure semiconductor to make it n-type semiconductor, it donates one free electron to the crystal, leaving a positive charge on the donor atom, the donated electron remains in the crystal in free state. As the charge on the donor ion is equal and opposite to the charge of the electron, the crystal itself remains electrically neutral. With the same reasoning, p-type semiconductor is also electrically neutral.