Room-temperature relaxor ferroelectricity and photovoltaic effects in SnTiOx/Si thin film heterostructures

摘要

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