Structural properties of epitaxial SrTiO3 thin films grown by molecular beam epitaxy on Si(001)

Abstract

This work reports on the structural properties of an epitaxial SrTiO3 (STO) layer grown by molecular beam epitaxy on a Si(001) substrate with a two step process. The study, which includes a complete characterization of large scale plane-view images of the STO layer, is based on a careful analysis of x-ray spectra and transmission electron microscopy images. The STO layer presents a good crystalline quality and a slight texturation related to the presence of extended defects. A thin Ti-rich amorphous silicate layer (thickness ≈1.3nm) is formed at the interface between the STO and the Si substrate, evidencing the thermodynamic instability of the STO/Si interface. The difference between the thermal expansion coefficients of Si and STO is shown to be at the origin of an increased in-plane lattice parameter (3.927Å) of the STO layer as compared to its bulk value (3.905Å). This effect of differential thermal expansion is expected to be responsible for the formation of at least part of the extended defects of the STO layer.