Optical revelation of defects in epitaxial barium titanate films


Allying epitaxial strain and synthesis conditions allow for the introduction of specific point defects in perovskite oxide films. In ferroelectric films, such defects lead to essential polar and electronic properties, which can enable advanced applications. Here, oxygen-vacancy-related defects are studied by investigation of optical constants in a broad spectral range of 0.75-8.8 ev in epitaxial ferroelectric BaTiO3 films. It is demonstrated that the defects produce in-gap states and internal electric field, which are manifested by an additional optical transition below the gap and significant blueshifts of the interband transitions, correspondingly. The formation and out-of-plane alignment of dipolar (Ti3+ - Vo) defect complexes can be responsible for this behavior. 

Figure: Second derivative of the imaginary part of the dielectric function in oxygen-deficient film (green) and reference crystal (blue). The out-of-plane and in-plane dipolar (Ti3+ - Vo) complexes are also schematically illustrated.