Photon recycling in semiconductor lasers

In a suitably designed semiconductor laser, spontaneously emitted photons with energies above the absorption edge can be reabsorbed in the active layer and can decrease the current density that must be supplied to reach the lasing threshold. The magnitude of the threshold reduction is estimated to be about 20% in a GaAs double-heterostructure laser at room temperature. © 1974 American Institute of Physics.