Electronic structure of SrTi1-x Vx O3 films studied by in situ photoemission spectroscopy: Screening for a transparent electrode material

This study investigated the electronic structure of SrTi1-xVxO3 (STVO) thin films, which are solid solutions of strongly correlated transparent conductive oxide (TCO) SrVO3 and oxide semiconductor SrTiO3, using in situ photoemission spectroscopy. STVO is one of the most promising candidates for correlated-metal TCO because it has the capability of optimizing the performance of transparent electrodes by varying x. Systematic and significant spectral changes were found near the Fermi level (EF) as a function of x, while the overall electronic structure of STVO is in good agreement with the prediction of band-structure calculations. As x decreases from 1.0, spectral weight transfer occurs from the coherent band near EF to the incoherent states (lower Hubbard band) around 1.0-1.5 eV. Simultaneously, a pseudogap is formed at EF, indicating a significant reduction in quasiparticle spectral weight within close vicinity of EF. This pseudogap seems to evolve into an energy gap at x=0.4, suggesting the occurrence of a composition-driven metal-insulator transition. From angle-resolved photoemission spectroscopic results, the carrier concentration n changes proportionally as a function of x in the metallic range of x=0.6-1.0. In contrast, the mass enhancement factor, which is proportional to the effective mass (m∗), does not change significantly with varying x. These results suggest that the key factor of n/m∗ in optimizing the performance of correlated-metal TCO is tuned by x, highlighting the potential of STVO to achieve the desired TCO performance in the metallic region.