Frequency dispersion of dielectric coefficients of layered TlGaS2 single crystals

Frequency dependence of the dissipation factor tanδ, the permittivity ɛ, and the ac conductivity σac across the layers in the frequency range f=5×104−3×107 Hz was studied in layered TlGaS2 single crystals. A significant dispersion in tanδ was observed in the frequency range 106−3×107 Hz. In the range of frequencies studied, the permittivity of TlGaS2 samples varied from 26 to 30. In the frequency range 5×104−106 Hz, the ac conductivity obeyed the f0.8 law, whereas for f>106 Hz σac was proportional to f2. It was established that the mechanism of the ac charge transport across the layers in TlGaS2 single crystals in the frequency range 5×104−106 Hz is hopping over localized states near the Fermi level. Estimations yielded the following values of the parameters: the density of states at the Fermi level NF=2.1×1018 eV−1 cm−3, the average time of charge carrier hopping between localized states τ=2 µs, and the average hopping distance R=103 Å.