Intrinsic carrier scattering mechanism in anataseTiO2investigated by ultraviolet-pump terahertz-probe spectroscopy

Abstract

We measured the optical conductivity $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\sigma}}(\ensuremath{\omega})$ spectra caused by photocarriers in anatase $\mathrm{Ti}{\mathrm{O}}_{2}$ by applying ultraviolet-pump terahertz-probe spectroscopy on epitaxially grown thin films. Drude model analyses of $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\sigma}}(\ensuremath{\omega})$ spectra reveal that, in the terahertz region, the reduced mass ($\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{m}$) of the carriers is greater and their damping constant ($\ensuremath{\gamma}$) is smaller than those in the infrared region. With regard to the extended Drude model, these differences can be attributed to the frequency dependence of $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{m}$ and $\ensuremath{\gamma}$ originating from carrier-phonon scatterings. Furthermore, the interaction between carriers and Ti-O stretching modes in the $500--1000\ensuremath{-}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ region strongly influences the intrinsic carrier scattering mechanism in anatase $\mathrm{Ti}{\mathrm{O}}_{2}$.