Improved Stability of Porous Silicon in Aqueous Media via Atomic Layer Deposition of Oxides

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In this work, porous silicon (PSi) samples were conformally coated with ultrathin films of aluminum oxide (Al 2 O 3 ) and hafnium oxide (HfO 2 ) using atomic layer deposition (ALD) to passivate their internal surface and improve their overall stability in aqueous media. Their porosity and optical properties were characterized before and after ALD treatment. The stability over time in aqueous media of the ALD passivated porous layers was then evaluated and compared to PSi layers oxidized at 800 °C (PSiO 2 ), which is a treatment widely used in the literature for biosensing applications. The ALD oxide-covered samples performed equally to the oxidized PSi samples, but exhibited a higher mean refractive index, which results in a better contrast. These improved optical properties resulted in a signal exhibiting a significantly decreased noise. This in turn leads to a theoretical limit of detection improved by a factor 13 and 16 for PSi/Al 2 O 3 and PSi/HfO 2, respectively, compared to the standard PSiO 2 . This could thus result in an improved sensitivity for biosensing applications.

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