Activated impurity states in the incommensurate phase of ferroelectric semiconductor TlInS₂

The effect of annealing within the incommensurate phase on the dielectric function ε of the TlInS₂ single crystals has been investigated. It is shown that the effect of annealing is very close to the effect of doping by electrically active impurity La. The inference is made that the correlation between observed effects in annealed and doped crystals is conditioned by the internal electric fields induced by the activation (polarization) of native defects during the annealing procedure. The investigations of the second harmonic generation in undoped TlInS₂ crystal and the pyrocurrent in TlInS₂:La confirms the proposed model.