Using a perovskite oxide buffer layer on Ca₂Nb₃O₁₀ nanosheets for the epitaxial growth of Pb(Zr_0.52Ti_0.48)O₃ for electrode-free thin films

Ca₂Nb₃O₁₀ nanosheet layers were deposited on Gallium Nitride (GaN)-on-Si substrates by the Langmuir-Blodgett method to obtain (001)-oriented growth of perovskite oxide thin films using pulsed laser deposition. We investigated the influence of 10 nm thick SrTiO₃, (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7 (LSAT) and LaMnO₃ films as buffer layers on the structural and ferroelectric properties of subsequentially grown Pb(Zr_0.52Ti_0.48)O₃ (PZT) films, which may be used as gate capacitors in high power GaN devices. Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray-Diffraction and in-plane polarization experiments were used to determine the influence of the oxide buffer layers on the PZT properties. Highly crystalline dense (001)-oriented PZT films with large in-plane polarizations were obtained using SrTiO₃ and LSAT as buffer layers. For SrTiO₃ and LSAT we observed an improvement of the structural and ferroelectric properties compared to PZT grown directly on the Ca₂Nb₃O₁₀ nanosheets and or using a LaMnO₃ buffer layer. The improved high-crystallinity PZT films grown on GaN using ultrathin buffer layers could enhance the performance of high-power semiconductor electronics or in other devices where there is a need for a ferroelectric layer without bottom electrode.