FROM MINUTES TO MONTHS - AGING OF POROUS SILICON SINGLE LAYERS AND SUPERLATTICES

The ageing of porous silicon under ambient conditions must be taken in to account in the design of optical devices using this material. The t ime dependence of the optical properties of porous silicon single laye rs and superlattices is studied in detail using reflectance spectrosco py. In the infrared the Si-H and Si-O vibrational modes are examined w hich reflect the state of the internal surfaces. The optical propertie s in the visible and ultraviolet spectral range are investigated as we ll. Spectra are recorded on time scales ranging from minutes to months after sample preparation. The observed changes of the optical propert ies are discussed. It is verified that the stability of porosity super lattice filters in time can be improved significantly by thermal oxida tion.