Spontaneous lifetime and quantum efficiency in light emitting diodes affected by a close metal mirror

The spontaneous lifetime and quantum efficiencies of dipoles placed close to a metal mirror are calculated. The importance of these effects is demonstrated in the recent experimental work on InGaAs-GaAs quantum-well light-emitting diodes (QW LEDs) in which the modulations rates were varied from 0.8 GHz to 1.4 GHz through the placement of a QW next to a Ag mirror (D.G. Deppe et al., 1990). Classical energy transfer theory is used to treat the spontaneous radiation of a QW in a semiconductor system. The spontaneous radiative lifetime and internal quantum efficiency are strongly affected by the location of the QW, which confines the dipoles, by the orientation of the dipole in the well, by the metal reflector material, and by the metal mirror thickness. In general, the internal quantum efficiency decreases when the dipole is closer to the metal, because of the nonradiative energy transfer from the dipole to the absorptive metal. The overall effect of closely spaced metal mirrors on the measurable external quantum efficiency, which is important for fast light emitting diode design, is presented.<
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