• Physico-chemical properties of the TlGaS2 - TlSbS2 system   [CET 2015]
  • Author(s)
  • Nazim Gasanov
  • The paper investigates replacementGa↔Sb in TlGaS2compound. TlGaS2 and TlSbS2 are wide-gap semiconductors having monoclinic and triclinic structures, respectively; they exhibit pronounced anisotropy of the physical properties,are optically active, and are characterized by high photosensitivity. TlGaS2compound melts at a temperature 884±5°C, and TlSbS2 - at 476±5°C. The results of differencial-thermografic analysis (DTA)of alloys ofthe TlGaS2-TlSbS2system have shown that it is quasi-binary section of the quaternary system Tl-Ga-Sb-S and the nature of interaction between the components is a eutectic diagram with limited range of solid solutions. Eutectic contains 90mol% TlGaS2 and melts at 480°C. The solubility limit of TlSbS2in TlGaS2 at the eutectic temperature is between 2.5 and 3mol%, solubility of TlGaS2in TlSbS2 - between 5 and 6mol%, at room temperature the length of the solid solutions TlGaxSb1-xS2 based on TlGaS2 is 0.985<х≤1 and based on TlSbS2 - 0≤ х<0.03. Samples of TlGaxSb1-xS2were examined withX-ray analysis as well, which was conducted by the method of Debye-Scherer. Diffraction patternsof solid solutions are similar to those of the initial compounds, for two-phase alloys they are represented by superposition of both. X-ray analysis gave the same resultas DTA: solid solutions based on TlGaS2compound contain up to ~1.5mol% TlSbS2, but the ones based on TlSbS2–up to ~3mol% TlGaS2. Electrical conductivity σac and dielectric permittivity ε of TlGa1-xSbxS2 single crystals, grown by the Bridgman-Stockbarger method, were studied by the resonance method with the alternating current at frequencies f = 5∙104÷3.5∙107Hz. Real part of the complex dielectric permittivity ε' of TlGa1-xSbxS2crystals in the studied frequency range had a weak dispersion. Unlike ε', the imaginary part of permittivity ε"and the dielectric loss tangent increased 3-3.5 times with the increase of the frequency from 5•104Hz to 3.5•107Hz. The dependence of conductivity on the frequency is changing according to the law σac(f) ~ f0,8. This suggests that in these crystals near the Fermi level hopping conduction over the localized states occurs. For TlGa1-xSbxS2crystals the density of localized states near the Fermi level NF = 5.9•1018÷6.8•1018eV-1cm-3 was determined, the average time of hopping from one localized state to another is τ = 5.7÷9.9•10-8s and jump distance is R = 77÷81Å, the energy distribution of localized levels is ΔE = 150÷154meV and the concentration of localized levels isNt= 8.8•1017÷1018cm-3. The photoelectric properties of TlGa1-xSbxS2 (x = 0, 0.005, 0.97 and 1.0)solid solutionswere investigate and it was determined that, based on these crystals highly sensitive photodetectors can be created. In the study of optical properties of TlGa1-xSbxS2 (x = 0, 0.005) solid solutions it was found that the optical absorption edge is formed by direct transitions with formation of excitons.
  • Physico-chemical properties, TlGaS2 - TlSbS2 system
  • References

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