Figure 4

Optical properties and ultimate efficiencies of core-shell nanoparticles with different coating thickness t (Au core/dielectric shell) placed on the front side of a 2 μm thick Si substrate with different period (P). The inner Au core is 120 nm and n is set as 3.4. (a) Reflectance spectra of a flat thick Si (2 μm, bare), a 120 nm Au sphere and core-shell nanoparticles on the 2 μm thick Si as a function of wavelength, the P is set as 400 nm. (b) Ultimate efficiency of core-shell nanoparticles on the 2 μm thick Si. (c) Magnified reflectance spectra of a 2 μm thick Si, a 120 nm Au sphere and core-shell nanoparticles on the 2 μm thick Si at long wavelength region; the inset illustrates the minimum reflectance of the 2 μm thick Si with core-shell nanoparticles locating on the surface. (d) Differential efficiency ∆η between the core-shell nanoparticles on a 2 μm flat Si and a 2 μm flat Si without nanoparticles. The dashed line is the differential value of efficiency between the core-shell nanoparticles on a 2 μm thick Si and a 120 nm Au sphere on a 2 μm thick Si and the P = 400 nm; the inset is the schematic in simulation.