Influence of the composition of TlGa$_{1-x}$Er$_x$Se$_2$ crystals on their dielectric characteristics and parameters of localized states

Frequency dependences of the real $(\varepsilon')$ and imaginary $(\varepsilon'')$ parts of the complex permittivity, the dielectric loss tangent $(\operatorname{tg}\delta)$, and the ac conductivity $(\sigma_{\mathrm{ac}})$ in frequency range$f$ = 5 $\cdot$ 10$^4$–3.5 $\times$ 10$^7$ Hz have been investigated for TlGa$_{1-x}$Er$_x$Se$_2$ crystals of various compositions. It has been established that the relaxation dispersion of $\varepsilon'$ and $\varepsilon''$ takes place for the studied crystals. The influence of the erbium content in the crystals on their dielectric coefficients has been studied. The ac conductivity of the TlGa$_{1-x}$Er$_x$Se$_2$ single crystals in the high-frequency range obeys the law $\sigma_{\mathrm{ac}}\sim f^{0.8}$, which is characteristic of the hopping mechanism of charge transfer over the states localized in the vicinity of the Fermi level. Parameters of the states localized in the band gap of TlGa$_{1-x}$Er$_x$Se$_2$ and the influence of the composition of the crystals on these parameters have been evaluated.