Editing Laser diode (section)

=== Generation of spontaneous emission ===
When an electron and a hole are present in the same region, they may [[recombination (physics)|recombine]] or ''annihilate'' producing a [[spontaneous emission]] — that is, the electron may re-occupy the energy state of the hole, emitting a photon with energy equal to the difference between the electron's original state and hole's state. (In a conventional semiconductor junction diode, the energy released from the recombination of electrons and holes is carried away as [[phonon]]s (lattice vibrations) rather than as photons.) Spontaneous emission below the [[lasing threshold]] produces similar properties to an [[light-emitting diode|LED]]. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating.