Editing Laser diode (section)

=== Double heterostructure lasers ===
[[File:Simple dh laser diode.svg|thumb|350px|Diagram of front view of a double heterostructure laser diode; not to scale]]

In these devices, a layer of low-[[bandgap]] material is sandwiched between two high-bandgap layers. One commonly-used pair of materials is [[gallium arsenide]] (GaAs) with [[aluminium gallium arsenide]] (Al<sub>x</sub>Ga<sub>(1-x)</sub>As). Each of the junctions between different bandgap materials is called a ''[[heterostructure]]'', hence the name ''double heterostructure'' (DH) laser. The kind of laser diode described in the first part of the article may be referred to as a ''homojunction'' laser, for contrast with these more popular devices.

The advantage of a DH laser is that the region where free electrons and holes exist simultaneously—the [[active laser medium|active region]]—is confined to the thin middle layer. This means that many more of the electron-hole pairs can contribute to amplification—not so many are left out in the poorly amplifying periphery. In addition, light is reflected within the heterojunction; hence, the light is confined to the region where the amplification takes place.