The fabrication of a patterned ZnO nanorod array for high brightness LEDs

Abstract

In this study, a patterned ZnO nanorod array was formed on the ITO layer ofGaN-based light-emitting diodes (LEDs), to increase the light extraction efficiencyof the LED. The bi-layer imprinted resin pattern was used for selective growthof the ZnO nanorod array on the ITO layer. Compared to conventional LEDsgrown on patterned sapphire substrate (PSS), the deposition of the blanket ZnOlayer on the ITO layer increased the light extraction efficiency of the LED byabout 10%. Further growth of the ZnO nanorod layer on the blanket ZnO layerincreased the light extraction efficiency of the LED by about 23%. In the casethat a patterned ZnO nanorod layer was formed on a blanket ZnO layer, thelight extraction efficiency increased by about 34%. These enhancements of thedevice were caused by modulation of the refractive-index in ZnO layers and thesurface roughening effects because of the unique design of the pattern, which wasnanostructure-in-nanopattern, resulting in the formation of many escape cones on the LEDsurface.