Terahertz dielectric spectra of (Ba,Sr)TiO3 thin films

Reflection and transmission spectra of Ba0.7Sr0.3TiO3 films with thicknesses of 36 and 800 mu m on the MgO substrate are measured in the frequency range from 8 to 1000 cm(-1) at room temperature. The dielectric parameters of the film material are derived using the simulation method. The dependence of the permittivity on the film thickness is determined. It is found that the absorption spectrum of the substrate strongly affects the calculated dielectric spectra of the film material. It is demonstrated that the simulation should be performed with the inclusion of the dielectric losses in the substrate in the subphonon frequency range.