What is bandgaps?

A band gap (also called an energy gap or forbidden gap) is an energy range in a solid where no electronic states can exist. In electronic band structure theory, band gaps generally result from diffraction of the electron quantum waves by the periodic crystal lattice. The size of the band gap determines whether a solid is a metal, semiconductor, or insulator. Semiconductors have a relatively small band gap, allowing them to conduct electricity under certain conditions, which makes them useful in transistors, diodes, and solar cells. Insulators have large band gaps, preventing the flow of electricity. Metals, on the other hand, have no band gap, allowing electrons to move freely.