Benjamin Meunier

GaAs Core/SrTiO3 Shell Nanowires Grown by Molecular Beam Epitaxy

We have studied the growth of a SrTiO3 shell on self-catalyzed GaAs nanowires grown by vapor-liquid-solid assisted molecular beam epitaxy on Si(111) substrates. To control the growth of the SrTiO3 shell, the GaAs nanowires were protected using an arsenic capping/decapping procedure in order to prevent uncontrolled oxidation and/or contamination of the nanowire facets. Reflection high energy electron diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were performed to determine the structural, chemical, and morphological properties of the heterostructured nanowires. Using adapted oxide growth conditions, it is shown that most of the perovskite structure SrTiO3 shell appears to be oriented with respect to the GaAs lattice. These results are promising for achieving one-dimensional epitaxial semiconductor core/functional oxide shell nanostructures.

Chemical reactivity between sol–gel deposited Pb(Zr,Ti)O3 layers and their GaAs substrates

We show how chemical interactions between the growing material and the substrate affect the crystallization of Pb(Zr,Ti)O3 (PZT) thin films on SrTiO3-templated GaAs substrates. A liquid PZT precursor (sol) is spin-coated on STO/GaAs pseudo-substrates grown by molecular beam epitaxy and crystallized by annealing under air. Complete crystallization of the PZT layers cannot be achieved due to significant oxidation of the GaAs substrate which enhances As diffusion through the structure and further formation of parasitic compounds containing Pb, Sr and As due to the strong chemical affinity between As anions and Pb and Sr cations. These mechanisms are extensively studied based on X-ray diffraction measurements carried out in situ during annealing and on transmission electron microscopy experiments including energy-dispersive X-ray analyses.

Ferroelectric Pb(Zr, Ti)O 3 thin layers on SrTiO 3 /GaAs

Ferroelectric epitaxial Pb(Zr, Ti)O3(PZT) layers were grown by pulsed laser deposition on SrTiO3/GaAs templates fabricated by molecular beam epitaxy. The templates present an excellent structural quality and the SrTiO3/GaAs is abrupt at the atomic scale. The PZT layers contain a- and c- domains, as shown by X-Ray diffraction analyses. Piezoresponse force microscopy experiments and macroscopic electrical characterizations indicate that PZT is ferroelectric. A relative dielectric permittivity of 164 is extracted from these measurements.