Page "Laser diode" Paragraph 6

The difference between the photon-emitting semiconductor laser and conventional phonon-emitting ( non-light-emitting ) semiconductor junction diodes lies in the use of a different type of semiconductor, one whose physical and atomic structure confers the possibility for photon emission.

These photon-emitting semiconductors are the so-called " 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.