Ferroelectric domain architecture and poling of BaTiO3 on Si

We investigate the ferroelectric domain architecture and its operando response to an external electric field in ${\mathrm{BaTiO}}_{3}$-based electro-optic heterostructures integrated on silicon. By noninvasive optical second-harmonic generation, we identify the preexistence of in-plane ($a$-) domains dispersed within a predominantly out-of-plane- ($c$-) oriented matrix. Monitoring the poling behavior of the respective domain populations, we show that the spontaneous polarization of these $a$-domains lack a predominant orientation in the pristine state, yet can be selectively aligned with an in-plane electric field, leaving the $c$-domain population intact. Hence, domain reorientation of a ferroelastic $c$-to-$a$ type was directly excluded. Such independent electrical control of ferroelectric $a$-domains in a $c$-oriented ${\mathrm{BaTiO}}_{3}$ film on silicon is a valuable platform for engineering multidirectional electro-optic functionality in integrated photonic devices.