Displaying Energy Scales

We run into difficulty when we attempt to display all three energies on one computer screen. If we use an energy that separates the conduction and impurity band energies, the valence band energy would be off the bottom of the screen — near your feet. On the other hand, if we display the energies of the conduction and valence band energies, the impurity band energy is so close to the conduction band energy that we cannot distinguish between them.

To see all three energies conveniently we need a compromise. Our solution is to display two energy scales. The one on the right shows the correct energies for the conduction and impurity bands while the one on the left displays valence and conduction band energies (see digram to the right). To help you remember the bands touch only the energy scale relevant to them.