Photoconductivity in BiFeO3 thin films

Abstract

The optical properties of epitaxial $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ thin films have been characterized in the visible range. Variable temperature spectra show an absorption onset near $2.17\mathrm{eV}$ , a direct gap ($2.667\pm 0.005\mathrm{eV}$ at $300\mathrm{K}$ ), and charge transfer excitations at higher energy. Additionally, we report photoconductivity in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ films under illumination from a $100\mathrm{mW}∕{\mathrm{cm}}^2$ white light source. A direct correlation is observed between the magnitude of the photoconductivity and postgrowth cooling pressure. Dark conductivities increased by an order of magnitude when comparing films cooled in 760 and $0.1\text{Torr}$ . Large increases in photoconductivity are observed in light.