Question

How does the energy gap in an intrinsic semiconductor vary, when doped with a pentavalent impurity?

• A. Energy gap increases
• B. Energy gap decreases
• C. Energy gap increases and then decreases
• D. remains unchhanged.

Answer 1

Answer: (B)

Energy gap decreases

When we add n-type or pentavalent impurities to the intrinsic semiconductor, the width of forbidden energy gap is reduced.

Due to the addition of donor atoms, allowable energy levels are introduced at a small distance below the conduction band. These new allowable energy levels are discrete .The forbidden gap(Eg) is only 0.01 eV of Ge and 0.05 eV for Si at room temperature.