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

In conventional light-emitting diodes (LED's), the external efficiency is l imited by total internal reflection at the semiconductor-air interface. The problem can be overcome by the concept of the nonresonant cavity LED, whic h is an LED with a textured top surface and a rear reflector. The surface i s textured using natural lithography, A monolayer of randomly positioned po lystyrene 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 distributio n of the spheres on the surface and the etching depth. Using optimized text uring conditions, we have realized un-encapsulated top-emitting oxide-confi ned GaAs/AlGaAs nonresonant cavity LED's with an external quantum efficienc y of 40%.