Light transmission through periodic sub-wavelength textured surface

Using the rigorous coupled-wave analysis method, we present a detailed study about the light transmission through periodic sub-wavelength textured surfaces. We investigate to what extent and under what conditions these textured surfaces are equivalent to a multilayer dielectric coating from the perspective of reversibility and azimuthal symmetry of the reflected and transmitted light. Our analyses show that this is completely determined by the relative size between the reciprocal lattice period of the textured surface structure and the wavevectors of the reflected and transmitted waves in the dielectric materials. It is found that these analyses can be used to determine the optimal surface texture which provides the best light trapping for solar cells in terms of the total internal reflection occurring in the high-index medium at incidence angles larger than the nominal critical angle. We also perform calculations for the antireflective characteristics of these sub-wavelength textured surfaces and find that an optimized surface texture can generally give quite small reflectance in a wide spectral and angle range, but for the current texture design its performance at higher incidence angles is usually poorer than an optimized multilayer AR coating with graded index along the thickness direction.