We present a reflection-type terahertz time-domain spectroscopic ellipsometry (THz-TDSE) technique for measuring the complex dielectric constants of thin-film materials without replacement of the sample. THz-TDSE provides complex dielectric constants from the ratio of the complex amplitude reflection coefficients between p- and s-polarized THz waves. The measured dielectric constants of doped GaAs thin films show good agreement with predictions of the Drude model, even though the film thickness is of the order of a tenth of the penetration depth of the THz waves. In addition, we demonstrate the measurements of soft-phonon dispersion in SrTiO(3) thin films deposited on a Pt layer. The obtained dielectric constants agree well with the predictions of a generalized harmonic oscillator model.

The terahertz range dielectric response of polycrystalline TiO 2 (rutile) ceramics and rutile single crystals were investigated by analyzing infrared-active phonons by both Fourier-transform far-infrared (FT-FIR) reflectivity measurement and terahertz time-domain spectroscopy (THz-TDS). The dielectric functions at room temperature measured by THz-TDS are well expressed using the general harmonic oscillator model. We found that the imaginary part of the dielectric permittivity of the TiO 2 ceramic is threefold higher than that of the rutile single crystal at 300 K. The large dielectric loss is attributed to the additional damping of the A 2u mode or/and an increase in the phonon damping. The low-temperature dielectric loss of the rutile single crystals is exceedingly low. However, TiO 2 ceramics shows little temperature dependence. These results indicate that extrinsic scattering significantly affects the dielectric loss of the TiO 2 ceramics in the THz region.

HfO2 thin films with elemental substitutions were formed by chemical solution deposition. Bi substitution distorts the HfO2 lattice and increases the polarization value. (Bi,Nb) substitution compensates the charge balance to prevent the formation of oxygen vacancies. The relative dielectric permittivity of the HfO2 film with 5 mol % La, 5 mol % Bi, and 5 mol % Nb substitution under an applied DC field was observed to be up to 78. The constriction of the polarization–electric field (P–E) curve disappears at a temperature lower than that where the dielectric permittivity is maximum. The phase transition from the paraelectric tetragonal phase to the ferroelectric orthorhombic phase causes the constriction of the P–E curve to disappear. We consider that the high dielectric permittivity was due to the phase-transition-related phenomena.

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We synthesized orientation-controlled (100), (110), and (111) BaTiO3 films by the CSD method and revealed the dielectric properties the films.