Correct Answer - Option 3 : 5
Atoms having 5 valence electrons acts as donor impurities
Antimony is a donor impurity as it has five valence band electrons.
Atoms having 3 valence electrons acts as acceptor impurities
Boron and Indium are acceptor impurities.
When we add n - type or donor impurities to the semiconductor, the width of the forbidden energy gap in the lattice structure is reduced. Due to an addition of donor atoms, allowable energy levels are introduced a small distance below the conduction band. These new allowable levels are discrete because the added impurity atoms are placed far apart and hence their interaction is small.
