Microstructural and electrical properties of ferroelectric/ZnO heterostructures

The microstructural and electrical properties of ferroelectric/ZnO heterostructures fabricated on SrTiO₃ substrates by pulsed laser deposition (PLD) were investigated. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) were employed to characterize the orientation of the samples. On ferroelectric oxide surfaces of (001) and (111) orientations, both of ZnO films followed c-axial direction. For the former, twin-domain structure would result in a smaller mismatch of about -1% by the epitaxial relation of ZnO[110]//BaTiO₃<110>. On (111) surfaces, single-domain ZnO films were observed with the in-plane orientation ZnO[100]//BaTiO₃[110] although 30deg domain rotation in the in- plane direction of the ZnO epilayer respect to the perovskite surfaces induced very large mismatch of about -15%. The all- epitaxial metal-ferroelectric-semiconductor (MFS) structures of ZnO/Pb(Zr_0.52Ti_0.48)O₃/SrRuO₃ were deposited on SrTiO₃(111) substrates due to the cube-on-cube epitaxial relationship between ferroelectric, SrRuO₃ electrode and substrates. Capacitance- voltage (C-V) measurements showed a ferroelectric window, indicating that the structures can achieve memory performance. The improvement of MFS inversion characteristics could be mainly due to good ferroelectric/ZnO interface.