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

Options

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

D

Explanation

Sample X is an intrinsic semiconductor. Impurity level is not shown. Hence it is not doped.
Sample Y is an n-type semiconductor, because the impurity energy level Iies just below the conduction band. It is doped with fifth group impurity (donor).
Sample Z is a p-type semiconductor because the impurity energy level lies just above the valence band and it is doped with a third group impurity (acceptor).