A diode laser passes an electric current through a semiconductor material, typically gallium arsenide, causing electrons and holes to recombine and emit photons through spontaneous emission. The photons then trigger additional electrons to emit more photons in stimulated. A laser diode (LD, also injection laser diode or ILD or semiconductor laser or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction. This is sandwiched in between a n-type GaAs and p-type GaAs layer as shown in Fig., InGaN, AlGaN), offering direct bandgap emission in the violet, blue, and green spectrum. There is a partially reflective surface at the P end and a highly reflective surface at the opposite (N) end.
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