Linear and nonlinear dielectric properties of BaTiO$_3$/Si film heterostructures prepared by pulsed laser deposition

Heterojunctions consisting of $n$-BaTiO$_3$ films 70 nm thick and $p$-silicon substrates with orientation (100) were fabricated by pulsed laser deposition. It was shown based on linear and nonlinear dielectric measurements that three sequential structural transitions between the cubic, tetragonal, orthorhombic, and rhombohedral phases with parameters somewhat differing from parameters of corresponding transitions in the BaTiO$_3$ single crystal occur in barium titanate films. The geometry of dielectric measurements differed when revealing particular phase transitions. A considerable increase in the heterojunction nonlinearity upon the transition of the film into the ferroelectric state was observed.