The combination on the same wafer of materials having different physical properties is a key challenge. In particular, functional oxides of the perovskite family are very attractive for applications in the micro-optoelectronic field since they present a variety of physical properties (ferroelectricity, ferromagnetism, superconductivity, high Pockels coefficients, …). They are classically grown on SrTiO₃ (STO) substrates, but molecular beam epitaxy (MBE) allows their epitaxy on Si and GaAs platforms, providing that specific interface engineering strategies are used. However, even in this case, chemical reactions between the growing oxide and the substrate strongly impact the epitaxy process and impose using specific growth procedures that are detrimental to the oxide crystal quality. Amongst the oxides that can be integrated on STO templates, Pb(Zr,Ti)O₃ (PZT) is of particular interest because of its high remanent polarization (P_r), its low coercive field (E_c) and its outstanding piezoelectric properties

In this contribution, we report the study of sol-gel prepared PZT thin films on STO/GaAs templates grown by molecular beam epitaxy (MBE). The spin-coated layers were calcined at 350°C under air for 5 minutes to dty the sol film. The crystallization of the PZT have been studied in function of post-annealings at three different temperatures ranging (405°C, 420°C and 510 °C). High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectroscopy (EDXS) have been used to study the structure and the chemical composition of the layers. High resolution HAADF images coupling to geometrical phase analysis (GPA) show that PZT is locally strained on the STO/GaAs during the first steps of crystallization. Complete crystallization of the PZT laeyrs cannot be achieved due to a significant oxidation of the GaAs substrate which enhances As diffusion through the structure and further formation of parasitic PbAs and SrAs compounds.               

ACKNOWLEDGEMENTS

We acknowledge Agence Nationale de la Recherche (ANR), program of investment for the future, TEMPOS project (n°ANR-10-EQPX-50) for having funded the acquisition of the NANOTEM platform (Dualbeam FIB-FEG FEI SCIOS system and TEM-STEM FEI Titan Themis equipped with the Super-X Chemistem EDX detectors) used in this work

Figures:

EDX mappings showing the elemental local compositions in PZT/STO/GaAs samples annealed at 420°C and 510°C

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EMC Abstracts - https://emc-proceedings.com/abstract/chemical-reactivity-between-sol-gel-deposited-pbzr-tio3-layers-and-their-gaas-substrates/