Integrating Surface Textures on ZnO Substrate for High Light Extraction Efficiency Light-Emitting Diode

Due to the large refractive index of ZnO material, light extraction efficiency (LEE) of ZnO based light-emitting diode (LED) is limited by the total reflection. We present a combined experimental and computational approach to study the effects of integrated surface textures on the efficiency of light extraction from the ZnO material. Hexagonal pyramids and pits textures were obtained by selective and anisotropic etching of O-polarity ZnO single crystal in HCl and KOH solutions, respectively. Dense hexagonal pyramids were integrated into the hexagonal pits via a two-step wet etching process. Ray-tracing simulations indicate that the substrate texturing can improve the performance of the ZnO based LEDs by enhancing the LEE and improving the light field uniformity. The integrated photoluminescence extraction was improved by a factor of 117% with respect to that of a planar ZnO single crystal through integrating the pyramids textures into the hexagonal pits.