The study of solid state physics and shortly thereafter semiconductors began after the early work regarding the X-ray diffraction of crystalline materials. Indeed, it is the periodic array of atoms within crystalline materials that gives rise to both the characteristic reflections from X-ray diffraction and the energy bands that ultimately give them their semiconducting properties. As opposed to non-crystalline solids, which typically have neither [26].

In short, many of the interesting and distinguishing properties of crystalline materials comes from the interplay between the electron wave functions and the periodic arrangement of the atoms in the material. In a crystalline material, the wavelength of the electron is short and therefore highly responsive to the local periodic arrangement of the atomic potentials. Whereas in a non-crystalline material, the electron-lattice interaction is significantly diminished. Somewhere between the two, in glasses for example, the wavelengths of light are long enough that they interact with an average order in the materials over much longer length scales, that the electron wavefunctions cannot.