Barrier height at(Ba,Sr)TiO3/Ptinterfaces studied by photoemission

Abstract

The interface formation of Nb-doped ${\text{SrTiO}}_{3}$ single crystals and $(\text{Ba},\text{Sr}){\text{TiO}}_{3}$ thin films with Pt has been studied by using photoelectron spectroscopy with in situ sample preparation. For the single crystal sample, a Schottky barrier height for electrons of 0.5--0.6 eV is determined after deposition of Pt in vacuum environment. After annealing in 0.05 Pa oxygen pressure, a strong increase in the barrier height to $\ensuremath{\ge}1.2\text{ }\text{eV}$ is observed. X-ray induced photovoltages of up to 0.7 eV are observed in this case and have to be taken into account for a proper determination of the barrier height. A subsequent annealing in vacuum reduces the barrier again. Hence, the barrier height can be reversibly switched between an oxidized state with a large barrier height and a reduced state with a low barrier height. Quantitative analysis of the barrier heights indicates that the changes are related to the changes of interfacial defect concentration. Due to the occurrence of a ${\text{Ti}}^{3+}$ related signal, the defects are identified as oxygen vacancies. The same effects are observed at interfaces between Pt and $(\text{Ba},\text{Sr}){\text{TiO}}_{3}$ thin films with a smaller absolute value of the barrier height in the oxidized state of $\ensuremath{\sim}1\text{ }\text{eV}$. Deposition of $(\text{Ba},\text{Sr}){\text{TiO}}_{3}$ onto a metallic Pt substrate also results in a barrier height of 1.0 eV.