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.