Room-temperature relaxor ferroelectricity and photovoltaic effects in tin titanate directly deposited on a 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 atomic-layer deposition 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 measurements reveal that the film is single-phase, preferred-orientation ferroelectric perovskite SnTiO3. Our films showed well-saturated, square, and repeatable hysteresis loops of around 3 mu C/cm(2) remnant polarization at room temperature, as detected by out-of-plane polarization versus electric field and field cycling measurements. Furthermore, photovoltaic and photoferroelectricity were found in Pt/SnTiO3/Si/SnTiO3/Pt heterostructures, the properties of which can be tuned through band-gap engineering by strain according to first-principles calculations. This is a lead-free room-temperature ferroelectric oxide of potential device application.