DIVERGENT MECHANISMS OF THE EFFECTS OF ELECTRON AND GAMMA IRRADIATION ON THE STRUCTURAL AND THERMOELECTRIC PROPERTIES OF Bi₂Te₃–Sb₂Te₃ THIN FILMS

Abstract

The advancement of space exploration and radioisotope thermoelectric generator (RTG) technologies demands the development of flexible thermoelectric materials capable of stable operation under extreme radiation environments. However, the divergent dynamic effects of corpuscular and photon-type radiation on the structural properties of chalcogenide solid solutions deposited on polymer substrates remain insufficiently understood. In this study, 25% Bi₂Te₃–75% Sb₂Te₃ thin films with a thickness of 0.790 μm, grown on polyethylene terephthalate (PET) substrates via thermal vacuum evaporation, were subjected to electron beam irradiation (up to 1×10¹⁵ e/cm²) and gamma irradiation (up to 1×10⁷ R). The morphological, structural, and electrophysical parameters of the specimens were systematically analyzed using atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and a two-probe measurement technique. The results revealed a fundamental difference in the degradation mechanisms depending on the nature of irradiation. At the critical electron fluence of 1×10¹⁵ e/cm², severe radiation damage and surface atom sputtering led to the formation of an amorphous-metallized surface layer, resulting in a sharp decrease in the Seebeck coefficient. In contrast, gamma irradiation fully preserved the surface morphology while generating homogeneous bulk Frenkel pairs via the Compton effect. This induced successive compensation and decompensation (defect coagulation) cycles strictly governed by the Pisarenko–Mott relation, with electrical conductivity dropping to 0.12×10³ Ω⁻¹·m⁻¹ at 1×10⁶ R and recovering to 0.84×10³ Ω⁻¹·m⁻¹ at 1×10⁷ R. It is concluded that gamma irradiation serves as a bulk defect engineering tool, whereas high-dose electron bombardment irreversibly degrades thermoelectric efficiency through surface erosion.