Metal Nanogrid for Broadband Multiresonant Light-Harvesting in Ultrathin GaAs Layers

Most plasmonic super absorbers use the excitation of surface plasmons to achieve perfect absorption in metal nanostructures. We present a design for an ultrathin metal-semiconductor-metal super absorber where light is mainly absorbed within a flat 25 nm thick GaAs semiconductor layer. The top metal layer is patterned as a two-dimensional grid with a subwavelength period and is covered with a thin embedding dielectric layer. We show numerically multiresonant absorption with low polarization and angular dependence. We experimentally demonstrate optical absorption above 80% over the 450-830 nm spectral range using a gold nanogrid. This work opens perspectives toward ultrathin active plasmonic optoelectronic devices and, in particular, highly efficient ultrathin solar cells. (Graph Presented).