Epitaxial SrTiO₃ Films with Dielectric Constants Exceeding 25,000

SrTiO₃ (STO) is an incipient ferroelectric perovskite oxide for which the onset of ferroelectric order is suppressed by quantum fluctuations. This property results in a very large increase in static dielectric constant from ~300 at room temperature to ~20,000 at liquid He temperature in bulk single crystals. However, the low-temperature dielectric constant of epitaxial STO films is typically a few hundred to a few thousand. In this talk, we will resolve this long-standing issue. Using all-epitaxial capacitor structure of the form n-STO/undoped STO/n-STO (001) prepared by hybrid molecular beam epitaxy, we demonstrate intrinsic dielectric constants of an unstrained STO (001) film exceeding 25,000 at low temperature. A careful analysis of the temperature-dependent dielectric constants reveals that the n-STO/undoped STO interface plays a vital role in determining the dielectric properties. Furthermore, using different dopant-types in n-STO, we reveal that it is the depleted side of the interface, i.e. n-STO that governs the overall measured dielectric constant [1]. A detailed growth study combined with the temperature- and frequency-dependent dielectric measurement will be presented.

References

[1] Z. Yang, D. Lee, J. Yue, J. Gabel, T.-L Lee, R. D. James, S. A. Chambers, B. Jalan, Proc. Natl. Acad. Sci. 119 (2022) e2202189119.