Design of patterned sapphire substrates in flip-chip LEDs for improvement of light-extraction efficiencies

Patterned sapphire substrates (PSSs) in flip chip light-emitting diodes (FC-LEDs) were designed to improve the light extraction efficiencies (LEEs). Two typical types were considered in the cross-section of the PSS pattern; an extruded type and a subtracted type. For pattern shapes in PSS, various polygonal pyramid pattern shapes were also considered, such as triangular-pyramid, square-pyramid, hexagonal-pyramid, circular-pyramids, in addition to hemispheres. Ray-tracing-based numerical simulations were performed for the LEEs of FC-LEDs with various PSSs. The optimal pattern shape for the high LEE was found to be the subtracted type triangular-pyramid shape, which is different from that of the optimal PSS patterns in conventional planar chip LEDs.