We fabricated a two-dimensional subwavelength structured (SWS) surface upon a crystal silicon substrate. The SWS surface was patterned by electron beam lithography and etched by an SF(6) fast atom beam. The SWS grating had a conical profile, the period was 150 nm, and the groove was approximately 350 nm deep. The reflectivity was examined at 2002500-nm wavelengths. At 400 nm the reflectivity decreased to 0.5% from the 54.7% of the silicon substrate. We also used HeNe laser light to examine the reflectivity as a function of the incident angle.
An ordered anodic porous alumina membrane has been used as a lithographic mask of SF6 fast atom beam etching to generate a 100 nm period antireflection structure on a silicon substrate. The antireflection structure consists of a deep hexagonal grating with 100 nm period and aspect ratio of 12, which is a fine two-dimensional antireflection structure. In the wavelength region from 400 to 800 nm, the reflectivity of the silicon surface decreases from around 40% to less than 1.6%. The measured results are explained well with the theoretical results calculated on the basis of rigorous coupled-wave analysis.
In this article, the light-trapping effect of textured back surface reflectors in thin-film Si solar cells is investigated. A unique substrate with a periodic dimple pattern has been developed by utilizing anodic oxidation of Al as a self-ordering process. n-i-p hydrogenated microcrystalline Si (μc-Si:H) cells fabricated on the Al substrate with a period of 0.9 μm show an improved infrared response compared to those fabricated on randomly textured substrates. A high short circuit current density of 24.3 mA/cm2 has been achieved in a 1-μm-thick μc-Si:H cell by adopting the patterned Al substrate.
Spectral emittance and thermal stability of two-dimensional W gratings are investigated to obtain high-temperature resistive selective emitters. Numerical calculations based on rigorous coupled-wave analysis are performed to determine the structural profile of gratings with good spectral selectivity. According to the determined parameters, two-dimensional W gratings composed of rectangular microcavities with the period of 1.0 μm are fabricated on single crystalline and polycrystalline W substrates. The grating shows a strong emission peak which can be explained by the confined modes inside the cavities. The grating with 200 nm wall thickness made from a single crystalline W shows very high thermal stability over 1400 K, while the polycrystalline grating is deformed at a high temperature because of the grain growth.
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