ACS Photonics   2016 年 3 卷 4 期

2016.04.20

We present a novel scheme for ultrabroadband and omnidirectional perfect absorbers with compact multilayer film structure. Our proposed device shows an average absorption of ???98% over a wide range of wavelengths ranging from 400 to 2000 nm. The ultrabroadband characteristics are achieved with strongly overlapped optical resonances by designing a tandem structure composed of three absorptive materials, while the overall structure features a graded refractive index profile to obtain a wideband antireflection property. In addition to the high efficiency and ultrabroadband absorption, our perfect absorbers exhibit a great angular tolerance up to 60?°, which is attributed to not only relatively broad resonances but also negligible propagation phase shifts in ultrathin highly absorbing layers. Lastly, we explore the effect of the number of semiconductor-metal stacks on the performance of the absorber. The presented approach can have tremendous potential for various applications, such as solar-thermal energy harvesting, thermoelectrics, detection, and imaging.