Integration of epitaxial Pb(Zr_0.52Ti_0.48)O₃ films on GaN/AlGaN/GaN/Si(111) substrates using rutile TiO₂ buffer layers

The integration of ferroelectric layers on gallium nitride (GaN) offers a great potential for various applications. Lead zirconate titanate (PZT), in particular Pb (Zr0.52Ti0.48)O3, is an interesting candidate. For that a suitable buffer layer should be grown on GaN in order to prevent the reaction between PZT and GaN, and to obtain PZT with a preferred orientation and phase. Here, we study pulsed laser deposited (100) rutile titanium oxide (R-TiO2) as a potential buffer layer candidate for ferroelectric PZT. For this purpose, the growth, morphology and the surface chemical composition of R-TiO2 films were analyzed by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. We find optimally (100) oriented R-TiO2 growth on GaN(0002) using a 675 °C growth temperature and 2 Pa O2 deposition pressure as process conditions. More importantly, the R-TiO2 buffer layer grown on GaN/Si substrates prevents the unwanted formation of the PZT pyrochlore phase. Finally, the remnant polarization and coercive voltage of the PZT film on TiO2/GaN/Si with an interdigitated-electrode structure were found to be 25.6 μC/cm2 and 8.1 V, respectively.