Characterisation of porous silicon composite material by spectroscopic ellipsometry

摘要

Porous silicon materials are currently under intense investigation for optoelectronic applications. Spectroscopic ellipsometry (SE) was used to study the optical properties of layers of composite material composed by porous silicon and disperse red one (a red dye which is well known for its non-linear properties) in the UV-IR spectral range (0.75-4.5 eV). P-doped silicon substrate was first electrochemically etched in a dilute HF electrolyte solution in order to obtain porous silicon films. Then these films were oxidised to produce a thin (5 μm) transparent layer of SiO_2 on the silicon substrate with negligible optical anisotropy. After the oxidation, disperse red one (DR1) molecules diluted in a solution of THF (tetrahydrofurane) were introduced in the porous material. The DR1 is uniformly distributed inside the porous silica layer and the amount of dye was estimated by an effective medium approximation. The "orientation of the dye molecules was tested after poling by a static electrical field.