Design of out-coupling structures with metaldielectric surface relief

We propose an unconventional out-coupling structure consisting of two-dimensional periodic metal-dielectric patterns. Numerical simulations show that low orders of guided modes are extracted efficiently by the metal-dielectric pattern with a pitch size of ∼(λ/n) and pattern depth of <100 nm. Vertical GaN light-emitting diodes with optimized metal-ITO patterns exhibited extraction efficiencies enhanced by factors of 6.6 and 2.6 for perfect conductor and silver metals, respectively, as compared to a nonpatterned structure. The plasmonic absorption loss from the corrugated silver mirror accounts for the relatively smaller enhancement in extraction efficiency with the silver-ITO pattern. Furthermore, a double-sided outcoupling structure consisting of an upper GaN-air pattern and a bottom perfect conductor-ITO pattern exhibited a 40% enhancement in extraction efficiency as compared to the structure with single GaN-air pattern. We believe that deep understandings of the interaction between light and metaldielectric patterns will lead to improved device performances in various optoelectronic applications including high-efficiency light-emitting diodes.