From Minutes to Months: Ageing of Porous Silicon Single Layers and Superlattices

The ageing of porous silicon under ambient conditions must be taken into account in the design of optical devices using this material. The time dependence of the optical properties of porous silicon single layers and superlattices is studied in detail using reflectance spectroscopy. In the infrared the Si–H and Si–O vibrational modes are examined which reflect the state of thc internal surfaces. The optical properties in the visible and ultraviolet spectral range are investigated as well. Spectra are recorded on time scales ranging from minutes to months after sample preparation. The observed changes of the optical properties are discussed. It is verified that the stability of porosity superlattice filters in time can be improved significantly by thermal oxidation.