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 smounts of third and fifth group impurities while sample $Y$ 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

The correct option is D Sample $X$ is undoped while samples $Y$ and $Z$ have been doped with a fifth group and a third group impurity respectively.

There is no extra energy level in between conduction and valence bands, in sample $X$. Clearly, it is an intrinsic silicon, i.e. undoped silocon.

In sample $Y$, the extra energy level lies near the bottom of the conduction band, so it is a $N-$type semiconductor and has been doped with an element from the fifth group.

In sample $Z$, the extra energy level lies near the top of the valence band, so it is a $P-$type semiconductor and has been doped with an element from the third group.

Hence, $\left(D\right)$ is the correct answer.