Effect of Composition on the Electrical Properties of (TlInS2)1–x(TlGaSe2)х Multicomponent Solid Solutions

Abstract

We have synthesized the ternary compounds TlInS₂ and TlGaSe₂ and (TlInS₂)_1–x (TlGaSe₂)_х (x = 0.1, 0.2, 0.4) solid solutions. The phase composition and lattice parameters of their single crystals grown by directional solidification have been determined by X-ray diffraction. At room temperature, the crystals have a layered monoclinic structure with space group \(C_{{2{\text{h}}}}^{6}\left( {C2{\text{/}}c} \right)\). Their properties have been shown to vary systematically with composition. The real (ε') and imaginary (ε″) parts of the complex dielectric permittivity, dielectric loss tangent (tan δ), and ac conductivity (σ_ac) of the single-crystal TlInS₂-based solid solutions have been measured as functions of frequency across the layers of the crystals. Their dielectric properties have been measured by a resonance technique at ac electric field frequencies f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The observed hyperbolic decrease in tan δ with increasing frequency suggests that the solid solutions have conductivity losses. We have identified the hopping mechanism of charge transport in (TlInS₂)_1–x(TlGaSe₂)_х and determined parameters of localized states in the band gap of the crystals: Fermi-level density of localized states (N_F = 5.8 × 10¹⁸ to 1.9 × 10¹⁹ eV^–1 cm^–3), mean hop time (τ = 2 × 10^–7 s), mean hop distance (R = 86 Å), and the energy spread of the states localized in the vicinity of the Fermi level (ΔE = 47 meV). The parameters ε', ε″, tan δ, and σ_ac of the (TlInS₂)_1–x(TlGaSe₂)_х (x = 0.1, 0.2, 0.4) single crystals have been shown to increase with increasing TlGaSe₂ content.