Microcavity light emitting diodes as efficient planar light emitters for telecommunication applications

Light emitting diodes (LEDs) can be coupled to optical fibers and used in telecommunication applications. Compared to laser diodes, the coupling is usually small, due to the isotropic emission of the source, combined with the large refractive index difference between the semiconductor and the outside medium. However, it is possible to greatly enhance the optical extraction of a planar LED by placing the source inside a microcavity which optical thickness is close to the wavelength of the emitted light. Some elementary design rules of a microcavity light emitting diode (MCLED) are explained here, and are illustrated on a real GaAs/Al_xGa_1−xAs device emitting at 880 nm. The surface external quantum efficiency of this MCLED reaches 14% into air and 20.6% with an encapsulation into an epoxy lens. These values are about 10 times larger than for a usual LED and are in good agreement with theoretical values, calculated with a plane waves model. To cite this article: D. Ochoa et al., C. R. Physique 3 (2002) 3–14