Research Of Anti-reflective Nanostructures

Antireflective nanostructures have attracted enormous attention recently because they can dramatically suppress the reflection losses and increase transmission of light at the interface simultaneously over a large range of wavelength and a large field of view. In scientific research, it’s still ambiguous to choose the optimum theory to analyze the reflectance characteristics of the antireflective nanostructures in a given condition even though there’re so many theories related. While in practical application, antireflective nanostructures provide excellent performance and extensive potential applications in virtue of its high level of transmission, ultra wide band and broad angular scope. The main contents are as following.Firstly, we give some analysis of different theories and methods for the calculation of antireflective nanostructures: effective medium theory(EMT), Rigorous coupled wave analysis(RCWA), finite-difference time-domain(FDTD) method and finite element method(FEM). Secondly, we use different theories and methods to analyze reflectance dependence on some parameters of the antireflective nanostructure, such as the period(dimension), the height, refractive index of the substrate and the filling factor of the nanostructure. How to choose an appropriate theory and the reason is considered in given conditions. Based on our analysis and calculation, effective medium theory(EMT) is unsuitable for nanostructures with a dimension(period) much smaller than the incident wavelength, as higher order diffraction waves other than the zeroth order diffraction propagate here; Rigorous coupled wave analysis(RCWA) can only be used in rigorously periodic conditions because the boundary conditions must be periodic, no matter the dimension of period. Finite element method(FEM) can be used in any conditions but with an excessive computation consumption. Finally, a nanostructure with a-360nm-period, a-200nm-width and a-250nm-height is fabricated on the Si substrate utilize laser interference lithography and etching technique. The surface features are shown under a scanning electron microscope. And the reflectance characteristics are measured by a spectrophotometer and an ellipsometer. The experimental result is in consistent with the theoretical result that the reflectance decreases about 20% during 300 nm and 1000 nm in the appearance of the nanostructure.