The dielectric properties of 〈100〉-oriented epitaxial ${\mathrm{SrTiO}}_3$ films as used in high-${\mathit{T}}_{\mathit{c}}$ heterostructures have been studied as a function of temperature and applied electric field by using in situ grown heterostructures (Mg/${\mathrm{SrTiO}}_3$/${\mathrm{SrTiO}}_3$:Nb and Au/${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$/${\mathrm{SrTiO}}_3$/${\mathrm{SrTiO}}_3$:Nb). The dielectric behavior of these films is characterized by a rather low sample capacitance as compared to bulk single-crystal values and by occurrences of maxima in the capacitance-voltage and capacitance-temperature curves. The maximum attainable polarization was found to be 80 mC/${\mathrm{m}}^2$ at 4.2 K. Complementary measurements on single crystals of ${\mathrm{SrTiO}}_3$ and ${\mathrm{SrTiO}}_3$:Nb reveal that the behavior of these ${\mathrm{SrTiO}}_3$ thin films can be understood from the bulk properties with additional strong charge trapping at the film-substrate interface.

• Received 8 November 1993

DOI:https://doi.org/10.1103/PhysRevB.49.12095