Epitaxial integration of BaTiO3 on Si for electro-optic applications

Abstract

BaTiO3 (BTO) is a highly promising material for the fabrication of electro-optic (EO) modulators due to the large effective Pockels coefficient of the material, particularly in an epitaxial form. It also has the added benefit of being readily integrated on a Si material platform via a SrTiO3 template. These two characteristics make epitaxial BTO ideal for use in next generation silicon photonics applications. Being a ferroelectric, BTO has a unique crystallographic direction in which the ferroelectric polarization points. For EO modulators, because the polarization direction controls the coupling between light and an external electric field, it is important to understand how different growth methods and subsequent processing affect the direction of the ferroelectric polarization. Certain electro-optic devices may require polarization to be in the plane of the film (in-plane switching liquid crystal devices), while other applications may require it to be normal to the plane of the film (Mach–Zehnder modulator). Here, we review the growth of epitaxial BTO on Si by a variety of deposition methods including molecular beam epitaxy, pulsed laser deposition, and RF sputtering. We summarize the resulting BTO film structure and quality based on the reported characterization results. We also discuss EO measurements of basic devices made from this material platform where such data are available.