Ultra-high efficiency light-emitting-diode arrays

An approach to increasing the escape probability for light-emitting diodes (LEDs) is proposed which involves the angular randomization by elastic scattering of the photons from a textured semiconductor surface. The approach has two components: (i) separation of thin-film heterojunctions from the growth substrate using the epitaxial liftoff (ELO) technique, and (ii) nanotexturing of the thin-film semiconductor interface by natural lithography. The LED structure is a conventional n/sup +/-AlGaAs/p-GaAs/p/sup +/-AlGaAs double heterostructure, grown over a 0.05 mu m thick AlAs release layer by organometallic chemical vapor deposition. The light versus current characteristics of the LEDs have been measured and modeled. A 9% external quantum efficiency from the untextured LED array was observed, transforming into a 30% external quantum efficiency following the surface texturing treatment. It is concluded that, by employing the principle of phase-space-filling in an improved device geometry, 56% efficient LED arrays can be expected.