  We have studied ferroelectricity and photovoltaic effects in atomic layer
deposited (ALD) 40-nm thick SnTiO$_{x}$ films deposited directly onto p-type
(001)Si substrate. These films showed well-saturated, square and repeatable
hysteresis loops with remnant polarization of 1.5 $\mu$C/cm$^{2}$ at room
temperature, as detected by out-of-plane polarization versus electric field
(P-E) and field cycling measurements. A photo-induced enhancement in
ferroelectricity was also observed as the spontaneous polarization increased
under white-light illumination. The ferroelectricity exhibits relaxor
characteristics with dielectric peak shifting from ca. T = 600 K at f = 1 MHz
to ca. 500 K at 100 Hz. Moreover, our films showed ferroelectric photovoltaic
behavior under the illumination of a wide spectrum of light, from visible to
ultraviolet regions. A combination of experiment and theoretical calculation
provided optical band gap of SnTiO$_{x}$ films which lies in the visible range
of white light spectra. Our study leads a way to develop green ferroelectric
SnTiO$_{x}$ thin films, which are compatible to semiconducting processes, and
can be used for various ferroelectric and dielectric applications.
