Room-temperature relaxor ferroelectricity and photovoltaic effects in tin titanate directly deposited on silicon substrate

Tin titanate (SnTiO₃) has been notoriously impossible to prepare as a thin-film ferroelectric, probably because high-temperature annealing converts much of the Sn²⁺ to Sn⁴⁺. In the present paper, we show two things: first, perovskite phase SnTiO₃ can be prepared by ALD directly onto p-type Si substrates; and second, these films exhibit ferroelectric switching at room temperature, with p-type Si acting as electrodes. X-ray diffraction (XRD) measurements reveal that the film is single-phase, preferred-orientation ferroelectric perovskite SnTiO3. Our films showed well-saturated, square and repeatable hysteresis loopsof around 3 μC/cm² remnant polarization at room temperature, as detected by out-of-plane polarization versus electric field (P-E) and field cycling measurements. Furthermore, photovoltaic and photoferroelectricity were found in Pt/SnTiO³/Si/SnTiO³/Pt heterostructures, of which properties can be tuned through band gap engineering by strain according to the first-principles calculations. This is a new lead-free room-temperature ferroelectric oxide of potential device application.