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

The electrodynamic properties of La-doped SrTiO3 thin films 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 films is observed. With decreasing oxygen partial pressure during the film 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 SrTiO3 system. Thermopower of the La-doped SrTiO3 thin films can be largely modulated from -120 to -260 V K-1, reflecting an enhanced polaronic mass of approximate to 3 < m(polron)/m < approximate to 4. The elemental vacancies generated in the TMO films grown at various P(O-2) influences the global polaronic transport, which governs the charge transport behavior, including the thermoelectric properties.