ELECTRICAL PROPERTIES OF Pb4Ga4GeSe12–Pb4Ga4GeS12 SOLID SOLUTION CRYSTALS
DOI:
https://doi.org/10.32782/pet-2025-2-15Keywords:
crystals, defects, conductivity type, resistivity, light absorption, band gapAbstract
The paper presents the results of studies on the electrical and optical properties of Pb4Ga4GeS12–Pb4Ga4GeSе12 crystals. The Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals corresponded to the compositional content of 10, 20, 30, 40 and 50 mol.% Pb4Ga4GeSе12. The semiconductor compounds Pb4Ga4GeSе12 and Pb4Ga4GeS12, as well as their solid solutions Pb4Ga4GeS12– Pb4Ga4GeSе12, crystallize in a tetragonal space group Р–421с and are promising materials for research in advanced areas of semiconductor materials science. These compounds combine the properties of several classes of semiconductors: classical semiconductors, thermoelectric materials, and nonlinear optical materials. Single crystals of Pb4Ga4GeS12 exhibit p-type conductivity, which is primarily associated with the presence of defects such as Pb, Ga, or Ge vacancies (VPb, VGa, VGe), or substitutional defects like PbGa and PbGe. In contrast, the solid solutions Pb4Ga4GeS12–Pb4Ga4GeSе12 containing 10–50 mol.% of Pb4Ga4GeSе12 demonstrate n-type conductivity. The main factors responsible for this conductivity type inversion are the decrease in band gap (Eg) and the increase in selenium vacancy (VSe) concentration with rising Pb4Ga4GeSе12 content. The non-monotonic dependence of the electrical resistivity of Pb4Ga4GeS12–Pb4Ga4GeSе12 on the Se concentration results from the dominance of different conduction mechanisms at various compositions. The initial increase in resistivity (from 0 to about 10 mol.% Pb4Ga4GeSе12) occurs because some sulfur atoms are replaced by selenium atoms, increasing the crystal lattice defect density and reducing carrier mobility. At concentrations around 20 mol.% Pb4Ga4GeSе12 and higher, the crystal lattice gradually transforms into a more thermodynamically stable structure similar to Pb4Ga4GeSе12, which leads to a decrease in resistivity. Moreover, the reduction of the band gap (Eg) further lowers the thermal activation energy of donor and acceptor centers, enhancing conductivity.
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