Answer
The structure of the energy bands shows how a semiconductor can behave like a metal with a change in temperature or pressure.
Work Step by Step
This is explained in Figure 42.19. In a semiconducting material, the energy gap is of moderate size, and the conduction band is mostly empty at low T.
With a rise in temperature, electrons can gain enough energy to hop into and partially fill the conduction band, which gives them a metallic band structure.
A change in pressure can also narrow the width of the band gap, accomplishing the same result.