Epitaxially Integrated Electro‐Optic KNbO 3 Thin Films on Silicon

The absence of a native electro‐optic effect in silicon remains a fundamental limitation for integrated photonics, motivating the integration of ferroelectric oxides as active materials. Here, we report the first epitaxial integration of KNbO 3 thin films on silicon, establishing a new materials platform for silicon‐integrated electro‐optics. Silicon integration of KNbO 3 has remained unexplored due to potassium volatility challenges during synthesis. Employing suboxide molecular‐beam sources assisted by in situ RHEED monitoring and guided by thermodynamic simulations, we establish an adsorption‐controlled growth window for phase‐pure KNbO 3 films. Temperature dependent x‐ray diffraction, optical second‐harmonic generation, piezo‐response force microscopy, and transmission electron microscopy aided by phase‐field simulations confirm high‐quality epitaxial films with sharp interfaces and structural phase transitions mirroring KNbO 3 single crystals. Electro‐optic measurements demonstrate a linear Pockels response with an effective electro‐optic response of 146 ± 14 pm V −1 at 1550 nm. Phase‐field simulations further predict that modest compressive strain can drive the electro‐optic response to ∼900 pm V −1 . Beyond KNbO 3 , this integration pathway provides access to the broader (K,Na)(Ta,Nb)O 3 family, opening pathways to harness their strong electro‐optic response, nonlinear optical response, piezoelectric response and ferroelectric properties for next‐generation silicon photonics and electronics beyond current BaTiO 3 ‐based approaches.