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

Options

A. Sample `X` is undopped while samples `Y` and `Z` have been dopped with the thirtd group and a fifth group impurity respectively
B. Sample `X` is undopped while both `Y` and `Z` have been dopped with the fifth group impurity
C. Sample `X` has been dopped with equal amount of third and fifth group impurities while sample `Y` and `Z` are undopped
D. Sample `X` is undopped while samples `Y` and `Z` have been dopped with the fifth group and a third group impurity respectively

Answer

D

Explanation

In sample `x` no impurity level seen, so it is undoped. In sample `y` impurity energy level lies below the conduction band so it is dopped with fifth group impurity. In sample `z`, impurity energy level lies above the valence band so it is dopped with third group impurity.