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. The donor level lies closely below the bottom of the conduction band. In the figure shown, below conduction band there are\[{{N}_{d}}\]donor levels per\[c{{m}^{3}}\]of energy\[{{E}_{i}}\]At low temperatures, small fraction of donors will be ionised and practically all donor levels will be filled with electrons. Note:\[\Delta E=({{E}_{C}}-{{E}_{i}})\]is called as ionisation energy of donors.