Editing Laser diode (section)

=== Direct and indirect bandgap semiconductors ===
The difference between the photon-emitting semiconductor laser and a conventional phonon-emitting (non-light-emitting) semiconductor junction diode lies in the type of semiconductor used, one whose physical and atomic structure confers the possibility for photon emission. These photon-emitting semiconductors are the so-called "[[Direct and indirect band gaps|direct bandgap]]" semiconductors. The properties of [[silicon]] and [[germanium]], which are single-element semiconductors, have bandgaps that do not align in the way needed to allow photon emission and are not considered ''direct''. Other materials, the so-called compound semiconductors, have virtually identical crystalline structures as silicon or germanium but use alternating arrangements of two different atomic species in a checkerboard-like pattern to break the symmetry. The transition between the materials in the alternating pattern creates the critical [[direct bandgap]] property. [[Gallium arsenide]], [[indium phosphide]], [[gallium antimonide]], and [[gallium nitride]] are all examples of compound semiconductor materials that can be used to create junction diodes that emit light.

[[File:simple laser diode.svg|frame|right|Diagram of a simple laser diode, such as shown above; not to scale]]
[[File:Metal covered Laser diode switched on.jpg|thumb|left|A simple and low-power metal-enclosed laser diode]]