Question

In an n-type semiconductor, the donor energy level lies
A. at the center of the energy gap
B. below the conduction band.
C. just above the valence band
D. in the conduction band.

Answer 1

Hint:In the above question they have asked where does the donor level of n type semiconductor lie so as we know majority carriers are electrons but there may also be some holes this creates change of positions of energy levels.

Complete answer:
A semiconductor is a substance which allows partial flow of electric current through it. The number of free electrons which are present in the semiconductors are less as compared to that of the conductor. Semiconductors which are used in electric circuits can have N type and P type of semiconductor.

In the N type of semiconductor the donor energy lies just below the conduction band and in the p type of semiconductor the donor energy lies slightly above the conduction band.The level at top is conduction level and level below is valence band as given in figure.

\[{{\text{E}}_g}\] is energy gap between bands as shown in figure below and \[\Delta E\] is energy gap between donor level and conduction band therefore as we can see in figure we can conclude that \[\Delta E < \dfrac{{{{\text{E}}_g}}}{2}\] so the donor level lies just below conduction band.

Therefore the answer is option B.

Note:-In an n-type semiconductor, pentavalent impurity from the V group is added to the pure semiconductor. Examples of pentavalent impurities are Arsenic, Antimony, Bismuth etc. The pentavalent impurities provide extra electrons and are termed as donor atoms. Electrons are the majority charge carriers in n-type semiconductors.