Silicon with various structural morphologies is widely used for solar cells and other optoelectronic devices. We present a new chemical etching process for nanoscale texturing of Si surfaces, which results in an almost complete suppression of the reflectivity in a broad spectral range, leading to black Si surfaces. The chemical etching process affects only the topmost 200-300 nm of the Si material. And it isn't dependent on the Si surface orientation and doping. Besides, the antireflective performance of reacted Si surface will highly improve with silver catalyst effect. Hence, it can be applied to various structural forms of bulk silicon as well as to thin Si films. The optical properties of various black Si samples are presented and discussed in correlation with the surface morphology, which are measured by atomic force microscope.
The fabrication of high-quality large-area thick Al films with a thickness around 10 μm or even more is one of the most important factors to realize high-performance large-size echelle gratings. During the deposition process of large-area Al films, Al film quality generally exhibits a different behavior along the radius (R) direction, which seriously affects the performance of echelle gratings. In this study, for the first time, we investigate the radial-quality uniformity of large-area (R=400 mm) thick (>10 μm) Al films in detail. We not only analyze the radial-quality difference of Al films prepared by the traditional electron-beam evaporation process, but also significantly improve the radial-quality uniformity of large-area thick Al films by using a coevaporation process. By comparing two kinds of film coating processes, we clarify the origin of the radial-quality difference of Al films, and prepare large-area thick Al films with excellent radial-quality uniformity.