Enhanced thermoelectric power factor in BiSnTe alloy thin films via post-annealing: a structural and electrical study

This study investigates the impact of post-annealing time duration on the structural, electrical, and thermoelectric properties of BiSnTe alloy thin films grown using a simple thermal evaporation route. X-ray diffraction (XRD) analysis revealed that grown samples exhibited a cubic rock-salt structure, with enhanced crystallinity and increased lattice parameters as post-annealing time extended from 1 to 4 h. Raman spectroscopy indicated shifts in vibrational modes toward lower wavelengths, attributed to the redistribution of Bi atoms within the SnTe matrix during annealing. Scanning electron microscopy (SEM) demonstrated uniform surface morphology with grain growth corresponding to longer annealing times. Electrical measurements showed a decrease in charge carrier concentration from 7.62 × 10¹⁹ cm⁻³ to 6.34 × 10¹⁹ cm⁻³ and a reduction in mobility from 202.21 cm²V⁻¹ s⁻¹ to 126.89 cm²V⁻¹ s⁻¹. This was correlated with grain growth, defect formation, and strain relaxation. The Seebeck coefficient increased the as-grown BiSnTe alloy thin film to 4 h post-annealed sample from 13.30 to 81.3 mV/K due to the reduction of carrier concentration with increasing the post-annealing duration. The corresponding thermoelectric power factor reached 1461 µWm⁻¹ K⁻², demonstrating the material's potential for thermoelectric applications.