40% efficient thin-film surface-textured light-emitting diodes by optimization of natural lithography

40% efficient thin-film surface-textured light-emitting diodes by optimization of natural lithography ■

Reiner Windisch, Barun Dutta, Maarten Kuijk, A. Knobloch, S. Meinlschmidt, S. Schobert, P. Kiesel, Gustaaf Borghs, Godfried Dohler, P. Heremans

Abstract ■

In conventional light-emitting diodes (LED's), the external efficiency is limited by total internal reflection at the semiconductor-air interface. The problem can be overcome by the concept of the nonresonant cavity LED, which is an LED with a textured top surface and a rear reflector. The surface is textured using natural lithography, A monolayer of randomly positioned polystyrene spheres acts as a mask for dry etching. We present details about the optimization of the parameters of the texturing process for GaAs/AlGaAs LED's, The studied parameters are the size of the spheres, the distribution of the spheres on the surface and the etching depth. Using optimized texturing conditions, we have realized un-encapsulated top-emitting oxide-confined GaAs/AlGaAs nonresonant cavity LED's with an external quantum efficiency of 40%