Porous silicon multilayers for sensing by tuneable IR-transmission filtering

The suitability of porous silicon multilayer (PSM) structures in sensing applications has been investigated. Bragg-filters as well as Fabry–Perot interference structures were prepared using controlled anodisation of silicon in an HF electrolyte by a tight control of structural parameters. The relationship between process parameters (current density and etching time) and final structural parameters (porosity and layers thickness) was established earlier by means of spectroscopic ellipsometry and optical modelling. Transmission filtering in the NIR range as well as reflective type operation in wet ambient was demonstrated in the visible range. On the example of coupled resonator structures we proved the slightly increasing porosity developed in the multilayer during subsequent anodisation steps. The shifting of the resonant peak positions by incorporated liquid in the pores can be monitored in situ enabling the dynamic, spatial analysis of pore filling or drying.