Britney's Guide to Semiconductor Basics Semiconductors Introduction Materials can be catagorised into conductors , semiconductors or insulators by their ability to conduct electricity. It is a popular belief that insulators do not conduct electricity because their valence electrons are not free to wander throughout the material. In fact they are free to move around, however, in an insulator there are as many electrons as there are energy levels for them to occupy. If an electron swaps place with another electron no change is made since electrons are indistinguishable. There are higher energy levels, but to promote the electrons to such a high energy levels requires an enormous voltage.
Metals conduct electricity easily.
In this case, the energy levels between the conduction and valence band are closely spaced and there are more levels than electrons so very little energy is required to find new energies for electrons to occupy. The resistivity of a material is measure of how difficult it is for a current to flow. The band theory of materials explains qualitatively the difference between these types of materials. Electrons occupy energy levels from the lowest energies upwards. However, some energy levels are forbidden because of the wave like properties of atoms in the material.