FDTD study of anti-reflective properties of photonic crystal slabs in silicon

Mercier, Thomas M., Krishnan, Chirenjeevi, Rahman, Tasmiat, Shaw, Peter J., Lagoudakis, Pavlos G. and Charlton, Martin D.B. (2020) FDTD study of anti-reflective properties of photonic crystal slabs in silicon. Freundlich, Alexandre, Sugiyama, Masakazu and Collin, Stephane (eds.) In Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IX. vol. 11275, SPIE.. (doi:10.1117/12.2544226).

Abstract

Nanostructuring for the purpose of reflectance reduction has been widely investigated for Silicon based solar applications. Bare Silicon surfaces reflect between 50 and 60 % of the incident light and are thus unsuitable for absorbing significant amounts of sunlight. A typical approach to addressing this is to use an anti-reflective coating on top of the Silicon which reduces reflectance via destructive interference. Since this interference is mainly dependent on the thickness of film this type of anti-reflection layer can only be optimized for a certain wavelength and thus is inherently limited. To reduce the reflectance over a broad range of wavelengths a structuring based approach is necessary. A common approach to implementing this is by wet etching the top surface of a crystalline solar cell to create pyramid structures based on the crystalline dependence of the etching process. Since this approach exploits the crystalline structure it is most suited for crystalline Si. Dry etching based nanostructuring can offer a high level of control over the resulting structure with the crystalline dependence being less concern. One approach is to etch cylindrical holes arranged in a periodic fashion into the top surface of the device to create a photonic crystal lattice. Here we present a systematic analysis of a photonic crystal slabs in Silicon and how the geometry affect the reflectance of the device. Lumerical's FDTD solution is used to vary the pitch, diameter and depth of the cylindrical holes making up the Photonic Crystal structure. The analysis reveals that air fill fraction and hole depth are the most significant determinants of the overall reflectance.

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Contributors

Author: Tasmiat Rahman

Author: Peter J. Shaw

Author: Pavlos G. Lagoudakis

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