Polaron Transport and Thermoelectric Behavior in La-Doped SrTiO3 Thin Films with Elemental Vacancies

Abstract

The electrodynamic properties of La-doped SrTiO 3 thin fi lms with controlled elemental vacancies are investigated using optical spectroscopy and thermopower measurement. In particular, a correlation between the polaron formation and thermoelectric properties of the transition metal oxide (TMO) thin fi lms is observed. With decreasing oxygen partial pressure during the fi lm growth ( P (O 2 )), a systematic lattice expansion is observed along with the increased elemental vacancy and carrier density, experimentally determined using optical spectroscopy. Moreover, an absorption in the mid-infrared photon energy range is found, which is attributed to the polaron formation in the doped SrTiO 3 system. Thermopower of the La-doped SrTiO 3 thin fi lms can be largely modulated from –120 to –260 μV K −1 , refl ecting an enhanced polaronic mass of ≈3 < m polron / m < ≈4. The elemental vacancies generated in the TMO fi lms grown at various P (O 2 ) infl uences the global polaronic transport, which governs the charge transport behavior, including the thermoelectric properties.