'''

A semiconductor is a material that has a resistivity value between that of a conductor and an insulator. The conductivity of a semiconductor material can be varied under an external electrical field. Devices made from semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices. Semiconductor devices include the transistor, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits. Solar photovoltaic panels are large semiconductor devices that directly convert light energy into electrical energy.

In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current can be carried either by the flow of electrons or by the flow of positively-charged "holes" in the electron structure of the material.

Silicon is used to create most semiconductors commercially. Dozens of other materials are used, including germanium, gallium arsenide, and silicon carbide. A pure semiconductor is often called an “intrinsic” semiconductor. The conductivity, or ability to conduct, of semiconductor material can be drastically changed by adding other elements, called “impurities” to the melted intrinsic material and then allowing the melt to solidify into a new and different crystal. This process is called "doping".

Explaining semiconductor energy bands

There are three popular ways to describe the electronic structure of a crystal.

• Band structure

Image:HAtomOrbitals.png| In a single H-atom an electron resides in well known orbits. Note that the orbits are called s,p,d in order of increasing circular current. Image:CovalentBond.png| Putting two atoms together leads to delocalized orbits across two atoms, yielding a covalent bond. Due to the Pauli exclusion principle, every state can contain only one electron. Image:Bändermodell-Potentialtöpfe.png| This can be continued with more atoms. Note: This picture shows a metal, not an actual semiconductor. Image:Ressauts et terrasses.png| Continuing to add creates a crystal, which may then be cut into a tape and fused together at the ends to allow circular currents. Image:Si-band-schematics.PNG| For this regular solid the band structure can be calculated or measured. Image:Electronic_band_diagram.svg| Integrating over the k axis gives the bands of a semiconductor showing a full valence band and an empty conduction band. Generally stopping at the vacuum level is undesirable, because some people want to calculate: photoemission, inverse photoemission Image:Wave packet (no dispersion).gif| After the band structure is determined states can be combined to generate wave packets. As this is analogous to wave packages in free space, the results are similar. Image:Diffusion rayleigh et diffraction.png| An alternative description, which does not really appreciate the strong Coulomb interaction, shoots free electrons into the crystal and looks at the scattering. Image:Semiconduttore intrinseco.png| A third alternative description uses strongly localized unpaired electrons in chemical bonds, which looks almost like a Mott insulator.