Abstract
We report on the fabrication, the characterization, and the optical simulation of a gold–silica nanocomposite and present its integration into a broadband anti-reflective coating (ARC) for a silicon substrate. The two-layer ARC consists of a nanocomposite (randomly distributed gold cluster in a silica matrix) and a pure silica film. We capitalize on the large refractive index of the composite to impose an abrupt phase change at the interface of the coating to diminish the light reflection from the substrate through the ultrathin nanocoating. The average reflectivity of the silicon can be reduced by such a coating to less than 0.1% in the entire visible spectrum. We experimentally and numerically prove that percolated nanocomposites with an overall thickness of 20 nm can provide anti-reflectivity up to near infrared (NIR). The ARC bandwidth can be shifted more than 500 nm and broadened to cover even the NIR wavelength by changing the volume filling fraction of the gold clusters. The angular sensitivity of thin ultrathin antireflective coating is negligible up to 60°. The present ARC could find applications in thermo-photovoltaics and bolometers.
Highlights
Reflection of light from the interface between two media is a property that is desirable in some optical devices such as mirrors, but it is mostly unfavorable
It is known that double layer dielectric film (e.g., SiO2 /TiO2 ) anti-reflective coating (ARC) can reduce the reflectivity of optical materials such as glass, quartz [25], or silicon as long as the materials with lower refractive indexes face the air [26]
In transparent dielectric coating, the optical phase changes that causes interference is run by gradual growth inside the layers
Summary
Reflection of light from the interface between two media is a property that is desirable in some optical devices such as mirrors, but it is mostly unfavorable. The trend to develop coatings—which reduce the reflection at the interfaces, known as antireflective coating (ARC)—has been progressing for many years In this context, in a classical theoretical proposal developed in 1879, Lord Rayleigh showed that the reflectivity from any surface can be lowered whenever the refractive index (RI) contrast between the media on adjacent sides of the interface is minimized [6]. An absorbing coating has been presented as a new ARC, which shows a strong reflection reduction (due to absorption) at optical frequencies [13,14] Such an approach is not useful for optical devices such as glasses and telescopes, they can find application in energy harvesting devices [13,15] and surface reflectance coloring [16]. There, the large metal particles act as scattering centers and thereby increase the light, which reaches the substrate [17,18,19,20,21]
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