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