The role of charge carriers in the memory effect in the incommensurate phase of the semiconducting ferroelectric Sn2P2Se6

The memory effect in the incommensurate phase of the semiconducting ferroelectric Sn2P2Se6 is studied by dielectric measurements. The mechanism of the memory effect is associated with the pinning of the incommensurate modulation by a charged, most probably dipolar, defect density wave. It is suggested that a defect density wave is formed by a recharging of certain ions in the crystal lattice. The spatial distribution of the defects is defined by the population of trapping levels in the band gap. Comparison of the shape and temperature behaviour of the memory effect anomaly with theory and additional experiments, such as measurement of the thermostimulated current and determination of the activation energy of the charge carriers by various techniques, showed that the memory effect for the most part originates in the modulated population of the charge carriers on trap levels in the band gap.