Editing Laser diode (section)

=== Quantum well lasers ===
{{main|Quantum well laser}}
[[File:Simple qw laser diode.svg|thumb|350px|Diagram of front view of a simple quantum well laser diode; not to scale]]

If the middle layer is made thin enough, it acts as a [[quantum well]]. This means that the vertical variation of the electron's [[wavefunction]], and thus a component of its energy, is quantized. The efficiency of a [[quantum well laser]] is greater than that of a bulk laser because the [[density of states]] function of electrons in the quantum well system has an abrupt edge that concentrates electrons in energy states that contribute to laser action.

Lasers containing more than one quantum well layer are known as ''multiple quantum well'' lasers. Multiple quantum wells improve the overlap of the gain region with the optical [[waveguide]] [[normal mode|mode]].

Further improvements in laser efficiency have also been demonstrated by reducing the quantum well layer to a [[quantum wire]] or to a ''sea'' of [[quantum dot]]s.