Question

The energy band diagrams for three semiconductor samples of silicon are as shown. We can then assert that

• A. Sample X is undoped while samples Y and Z have been doped with a third group and a fifth group impurity, respectively.
• B. Sample X is undoped while both samples Y and Z have been doped with a fifth group impurity.
• C. Sample X has been doped with equal amounts of third and fifth group impurities while samples Y and Z are undoped.
• D. Sample X is undoped while samples Y and Z have been doped with a fifth group and a third group impurity, respectively.

Answer 1

Answer: (D)

In sample $X$ no impurity level is seen, so it is undoped. In sample $Y$ impurity energy level lies below the conduction bond so it is doped with fifth group impurity. In sample $Z$, impurity energy level lies above the valence band so it is doped with third group impurity.