Electrochemical preparation of a rugate filter in silicon and its deviation from the ideal structure
Porous silicon single layers are formed by anodization of silicon in a hydrofluoric acid solution at different current densities. An accurate estimation of the etch rates and refractive indices is performed. The refractive index-depth profile of a porous silicon rugate filter (PSRF) prepared by sinu...
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Veröffentlicht in: | Journal of applied physics 2007-03, Vol.101 (6), p.063503-063503-6 |
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Hauptverfasser: | , , , |
Format: | Artikel |
Sprache: | eng |
Online-Zugang: | Volltext |
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Zusammenfassung: | Porous silicon single layers are formed by anodization of silicon in a hydrofluoric acid solution at different current densities. An accurate estimation of the etch rates and refractive indices is performed. The refractive index-depth profile of a porous silicon rugate filter (PSRF) prepared by sinusoidally modulating the current density during etch is investigated. The produced PSRF is found to have a periodic pseudo-sinusoidal variation of refractive index with depth. The sinusoidal current density waveform that was employed generates a nonideal refractive index-depth profile with an asymmetric period. It is found that this deformed refractive index profile affects the quality of the characteristic resonant peak of the rugate filter. A simple modification of the current density waveform can be implemented, which allows one to achieve a true sinusoidal refractive index-depth profile characteristic of a rugate filter. The modified current density waveform allows the generation of a PSRF with a low index contrast and a sharp resonant band. The ability of these structures to act as chemical vapor sensors is tested and compared with the existing literature. The filters exhibit a red-shift in the photonic feature upon exposure to saturated ethanol vapor. The modified signal does not impose a significant change on the filter sensitivity to ethanol vapor. |
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ISSN: | 0021-8979 1089-7550 |
DOI: | 10.1063/1.2710339 |