Influence of Germanium Substitution on the DC Electrical Properties and Energy Density of States in Pb_50−xGe_xTe₅₀ Ternary Chalcogenide Alloys

This study investigates the structural evolution and DC electrical properties of Pb50−xGexTe50 ternary chalcogenide alloys with varying germanium concentrations (x = 5, 10, 15, 20). Synthesized via the melt-quenching technique, the alloys were characterized using Scanning Electron Microscopy (SEM) and temperature-dependent electrical resistivity measurements within the range of 290–475 K. Microstructural analysis revealed that increasing Ge substitution significantly promotes matrix densification, reducing porosity and improving inter-granular connectivity. The DC conductivity exhibits a systematic increase with Ge content up to x = 15, attributed to the increased density of defect states. For instance, as Ge content increases from x = 5 to x = 15, the DC conductivity increases, corresponding to an activation energy (ΔE1) shift from 0.203 eV to 0.281 eV at high temperatures. However, for the sample with x = 20, a non-monotonic shift in conductivity parameters is observed, evidenced by a significant reduction in the pre-exponential factor ( σ 01 ) compared to the intermediate compositions, which indicates a alteration in the conduction pathways. The conduction data were analyzed using the Mott and Davis model, identifying three distinct mechanisms: hopping between localized states near the Fermi level at low temperatures, hopping within band-tail states at intermediate temperatures, and excitation into extended states at high temperatures. Furthermore, calculations of the density of states (DOS) indicated that Ge incorporation increases the density of extended and localized states while simultaneously narrowing the band tail width ( Δ E ), thereby reducing structural randomness. These findings highlight the efficacy of germanium doping in tuning the electronic structure of Pb-Ge-Te alloys, suggesting their suitability for advanced optoelectronic and semiconductor applications.