Theoretical and Experimental Estimations of Photon Recycling Effect in Light Emitting Devices with a Metal Mirror

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Abstract
The photon recycling effect in light emitting devices was estimated theoretically and experimentally. It was shown from the rate equation analysis that this effect is marked when the injection carrier density is lower than 1×1018 cm-3 and the factor given by the average photon lifetime of spontaneous emission multiplied by the optical confinement factor inside the active region is larger than 100 fs. The external efficiency in light emitting diodes (LEDs) is improved by one order of magnitude if this factor is increased to 1 ps by the strong optical confinement around the active region. This theoretical estimation well agreed with the experimental result in fabricated GaInAsP/InP LEDs having a relatively wide emitting layer and a metal mirror; the efficiency became 1.6–1.8 times higher when the factor for fabricated LEDs was longer than 100 fs. An LED that exhibits a high efficiency comparable to those of laser diodes will be realized by improving the reflectivity of the metal mirror to higher than 99%.