Abstract:We estimate high optical absorption in silicon thin film photovoltaic devices using triangular corrugations on the back metallic contact. We computationally show 21.9% overall absorptivity in a 100-nmthick silicon layer, exceeding any reported absorptivity using single layer gratings placed on the top or the bottom, considering both transverse electric and transverse magnetic polarizations and a wide spectral range (280 -1100 nm). We also show that the overall absorptivity of the proposed scheme is relatively insensitive to light polarization and the angle of incidence. We also discuss the implications of potential fabrication process variations on such a device.

We computationally demonstrate one-way optical transmission characteristics of a subwavelength slit. We comparatively study the effect in single layer and double layer metallic corrugations. We also investigate the effect of a dielectric spacer layer between double corrugations to control the volumetric coupling of plasmon and optical modes. We computationally show unidirectional transmission behavior with an ultrahigh contrast ratio of 53.4 dB at λ01.56 μm. Volumetric coupling efficiency through the nanoslit strongly depends on the efficient excitation of both the surface plasmon resonance and metal-insulator-metal waveguide modes. We show that the behavior is tunable in a wide spectral range. [6], and quantum dots [7]. Recent reports observe one-way transmission behavior in the absence of nonlinear or anisotropic materials [1,[8][9][10][11]. Lockyear et al. Keywords[8] showed that it is possible to implement one-way transmission devices operating at the microwave frequencies using asymmetric rectangular gratings. In a double layer asymmetric grating structure, the transmission of one direction is improved by a resonant diffraction grating while the periodicity of the opposite orientation sustains only higher order modes [8]. Utilizing a double layer diffraction grating structure, Zen et al. [9] demonstrated that contrast ratios above 100 can be achieved.Excitation of surface plasmon resonances by metallic gratings can be used to achieve enhanced transmission [12]. One-way transmission devices operating at telecommunication standard wavelengths have been realized exploiting plasmonic modes including the use of tunable plasmon resonances obtained on rectangular metallic gratings coated with nonlinear materials [13], asymmetric plasmonic gratings integrated in slot waveguides [14], and asymmetric rectangular diffraction gratings [1]. It was shown that transmission through subwavelength apertures can be enhanced by metallic gratings at the illuminated side of a subwavelength aperture which enables the coupling of surface plasmon modes with the aperture [15]. Moreover, both theoretical [10] and experimental [11] demonstrations of one-way transmission characteristics of asymmetric rectangular gratings coupled with a subwavelength aperture have been accomplished at microwave frequencies.In this paper, we present the design and analysis of a oneway transmission device operating at the telecommunication standard wavelengths with an ultrahigh contrast ratio. Our design achieves strong unidirectional characteristics by exploiting the one-way transmission property of double layer gratings coupled with the extraordinary transmission through a subwavelength slit. We also investigate the effect of the resonant coupling of the modes of the front-side and back-side diffraction gratings on one-way transmission characteristics. We demonstrate that by controlling the coupling between the gratings with a separating dielectric layer, an ultrahigh contrast ratio can be achieved.