30-PERCENT EXTERNAL QUANTUM EFFICIENCY FROM SURFACE TEXTURED, THIN-FILM LIGHT-EMITTING-DIODES

There is a significant gap between the internal efficiency of light-em itting diodes (LEDs) and their external efficiency. The reason for thi s shortfall is the narrow escape cone for light in high refractive ind ex semiconductors. We have found that by separating thin-film LEDs fro m their substrates (by epitaxial lift-off, for example), it is much ea sier for light to escape from the LED structure and thereby avoid abso rption. Moreover, by nanotexturing the thin-film surface using ''natur al lithography,'' the light ray dynamics becomes chaotic, and the opti cal phase-space distribution becomes ''ergodic,'' allowing even more o f the light to find the escape cone. We have demonstrated 30% external efficiency in GaAs LEDs employing these principles.