Space charges and size effects in semiconducting ferroelectric BaTiO3/SrTiO3 superlattices

A continuum theory is developed to investigate the effects of space charges and size on ferroelectric superlattices, treating the ferroelectric perovskites as wide band-gap semiconductors instead of insulators, making it possible to couple the distribution of polarization and space charges through Maxwell's equation. It is found that the space charges tend to accumulate near the superlattice interface, resulting in large electric field near the interface, and thus enhanced polarization and asymmetric hysteresis loop. It also eliminates the uniform polarization that would exist in the superlattice in the absence of space charges. The effect of superlattice thickness is also investigated, and good agreements with experiments are observed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3473821]