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

TL;DR

This study demonstrates room-temperature relaxor ferroelectricity and photovoltaic effects in SnTiOx/Si heterostructures, revealing their potential for green ferroelectric devices compatible with semiconductor processes.

Contribution

It reports the first observation of room-temperature relaxor ferroelectricity and photovoltaic effects in SnTiOx thin films directly deposited on silicon, with experimental and theoretical analysis of their optical properties.

Findings

Ferroelectric hysteresis with remnant polarization of 1.5 μC/cm² at room temperature.

Photo-induced enhancement of ferroelectric polarization under white light.

Ferroelectric photovoltaic behavior across visible to ultraviolet spectrum.

Abstract

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.