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 are demonstrated in the recent experimental work on InGaAs-GaAs quantum well light emitting diodes in which the modulations rates were varied from 0.8 GHz to 1.4 GHz through the placement of quantum well next to a Ag mirror [Deppe et al., Electron. Lett. 26, 1665, 1990]. Classical energy transfer theory is used to treat the spontaneous radiation of a quantum well in a semiconductor system. The spontaneous radiative lifetime and internal quantum efficiency are strongly affected by the location of the quantum well, 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 as discussed by Kuhn [J. Chem. Phys., 53, 101, 1970]. The overall effect of closely spaced metal mirrors on the measurable external quantum efficiency is presented, which is important for fast light emitting diode design.