Question

The energy band diagrams for three semiconductor sample of silicon are shown. It follows 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

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

When a pentavalent impurity is added to a semiconductor, it is called a donor impurity because it donates an electron which occupies a discrete energy level(shown by broken lines) just below the condition band, as in sample Y. Trivalent impurity, on the other hand, is called an acceptor impurity because the impurity atoms introduce unoccupied discrete energy levels just above the valence band, as in sample Z.