Controlling tetragonality and crystalline orientation in BaTiO₃nano-layers grown on Si

Abstract

A hybrid growth process was developed in order to epitaxially integrate nano-layers of the multi-functional perovskite BaTiO₃ onto Si(001) substrates. In particular, we combined molecular beam epitaxy (MBE) with radio-frequency sputtering. Due to its strong influence on the functional properties, the crystalline structure of the layers was thoroughly investigated throughout our study. MBE-grown seed layers are tetragonal and c-axis oriented up to a thickness of 20 nm. A transition into a-axis films is visible for thicker layers. When the seed layer thickness exceeds 6 nm, subsequently sputtered BaTiO₃ films are epitaxial. However, their crystalline structure, their orientation with respect to the substrate, and their morphology are strongly dependent on the deposition and post-deposition thermal budget. Consistently with their crystalline symmetry, thin MBE BaTiO₃ films are piezo- and ferroelectric with a spontaneous polarization perpendicular to the surface. Also for thick films, the functional response, as determined via piezo-force microscopy, is in good agreement with the structural properties.

Electro-Optical Modulation Based on Pockels Effect in BaTiO3With a Multi-Domain Structure

“…However, a multi-domain structure is usually formed during the fabrication of BaTiO 3 layers [17,18]. In the present work, we carefully investigate the influence of the multi-domain structure, as well as the waveguide rotation angle, on the EO modulation performance.…”

Development of new photonic devices based on barium titanate in silicon

“…Recently, IBM has demonstrated the integration of a ferroelectric BTO film on silicon exhibiting a strong linear EO effect with an effective Pockels coefficient of reff = 148 pm/V [47]. This value exceeds previous data reported for integrated LiNbO3 by at least a factor of five, and for strained Si by a factor of 100.…”

“…Furthermore, the resulting orientation of BTO film can vary from purely aaxis to c-axis orientations, through a mixture of a and c-axes oriented configurations [46]. Epitaxial growth of BTO films offers the possibility to select the direction in which the spontaneous polarization can appear depending on the desired application [47].…”

“…However, during the fabrication of thin-film BTO layers a multi-domain structure is usually formed [46,47]. In the present study, we carefully analyze the influence of the multi-domain structure, as well as the waveguide rotation angle, on the EO modulation performance.…”

“…Then, the fabricated samples were characterized at NTC facilities and this constant feedback between all partners was crucial to obtain the electro-optic (EO) modulation results that here are presented. 47 For the fabrication of active devices, the following general approach was followed, which relies on three main blocks:…”