question_answer

Which of the following statements is true for an n-type semiconductor?

A)  The donor level lies closely below the bottom of the conduction band

B)  The donor level lies closely above the top of the valence band

C)  The donor level lies at the halfway mark of the forbidden energy gap

D)  None of the above

Correct Answer: A

Solution :

The donor level is found only in n-type semiconductors. When the impurity of antimony is introduced, then each atom of germanium has an extra electron. The energy of these electrons is less than the least energy of conduction band and is greater than the highest value of energy of valence band. Thus, the electrons from a specific energy level below donor energy level. Donor level lies closely below the bottom of the conduction band as shown. Note: Mimmumdonor energy level is 0.05 eV for Si and 0.01 eV for Ge. By giving this much amount of energy to the electron they become free and so to the conduction band.