LMGP Séminaire interne : Catherine DUBOURDIEU-31 mars 2015 - Monolithic integration of complex oxides on semiconductors by MBE

Catherine DUBOURDIEU
Directeur de Recherche
Institut des Nanotechnologies de Lyon

Abstract

The ability to epitaxially grow the perovskite compound SrTiO₃ on Si by molecular beam epitaxy (MBE) opened up the route, 15 years ago, to the monolithic integration of functional oxides on a semiconductor platform. Studies in this field were boosted by the search in the early 2000’s for ultrathin crystalline high permittivity oxides in order to replace the conventional SiO₂-based gate oxide in advanced field-effect transistors. MBE provides unique advantages to precisely construct, almost atom by atom, the oxide/semiconductor interface. Interface engineering using Sr- or Ti-based passivation is employed for the epitaxial growth of SrTiO₃ templates on Si or GaAs substrates respectively. These templates are subsequently used to grow perovskite complex oxides, which offer a wide range of properties, such as piezoelectricity, pyroelectricity, ferroelectricity, magnetism, multiferroicity or specific electro-optic properties.

In this talk, I will review the challenges associated with the monolithic integration of complex oxides on a semiconductor and more particularly with the integration of ferroelectrics. I will present a study on BaTiO₃ films epitaxially grown on Si(001) and SiGe by MBE. Ferroelectricity – with reversible switching of the polarization - is evidenced by piezoresponse force microscopy with polarization pointing perpendicular to the silicon substrate. The nano-domain structure is discussed on the basis of geometrical phase analysis of HRTEM images. Size effects on the ferroelectricity of BaTiO₃ ultrathin films and nanostructures are addressed.

I will conclude with two perspectives. One deals with in situ coupling MBE and CVD/ALD techniques for developing new oxide growth routes. Another one deals with the integration of epitaxial ferroelectric oxides in low power logic devices.