Photoconductivity in ferroelectrics

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Abstract
A review of studies of photoconductivity in the ferroelectric-semiconductors SbSI and BaTiO3 is given and the results are discussed. In the short wavelength region of the spectrum there is an “extrinsic” photoconductivity of the ferroelectric due to the effect of the strong surface electric field on the nonequilibrium carrier lifetime. On the basis of stationary and kinetic photoelectric measurements the peculiarities of photoconductivity in the ferroelectric phase transition are considered. The anomalous behaviour of concentration, mobility and nonequilibrium carrier lifetime, and its relation with the substantial role of electron-phonon interactions and also with the large value and anisotropy of the dielectric permittivity, are discussed. Combined study of the photoelectric phenomena in SbSI, including measurements at low temperatures, resulted in the conclusion that there is a complicated system of energy levels in the energy gap of this substance; the data also leads to assumptions about the role of these levels in the photoelectric and photoferroelectric phenomena.