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Existing studies demonstrate that the main cause of the degradation of switching contacts during the operation of thermoelements based on bismuth telluride are the low strength properties of this material and the insuffi cient adhesion of the barrier metallization layer to the surface of the semiconductor branch. The objective of this paper is to study the phase composition, morphology, hardness and adhesive properties of the surface of the semiconductor thermoelectric branches Bi2Te3−Sb2Te3 (p-type conductivity) obtained by hot pressing, after various types of surface modifi cation. P-type semiconductor branches based on Bi2Te3–Sb2Te3 solid solution were obtained by cold and subsequent hot isostatic pressing in vacuum (10–2 Pa) of respective powders and annealing semiconductor material blanks at T = 570 K for 24 hours in vacuum (10–1 Pa). Surface modifi cation of semiconductor branches was carried out by mechanical polishing and subsequent electrochemical polishing or pulsed photon treatment with incoherent light. Mechanical polishing was performed on a carbide-silicon abrasive disc with different grain sizes (from Р2000 to Р5000), to obtain a mirror surface. Pulsed photon treatment was performed by means of the radiation of xenon lamps (wavelength 0.2–1.2 μm) in an Ar atmosphere under the following conditions: double irradiation with a set of pulses with a duration of 10–2 s in 0.8 s, which corresponds to the radiation energy reaching the sample (EP), ~ 80 J/cm2. Electrochemical polishing was carried out in the following electrolyte composition: KOH – 90 g/l; H2C4H4O6 – 65 g/l, distilled water 845 g/l. Nickel was used as the switching layer, and molybdenum was used as the barrier layer. The layered deposition of metallic layers (Mo and Ni) onto the prepared surfaces of semiconductor branches was applied by magnetron sputtering of the corresponding targets in Ar. The phase analyses were performed by X-ray diffractometry (Bruker D2 Phaser). The relief and surface roughness of the samples were studied by atomic force microscopy (NT-MDT Solver P47). The hardness of the samples was measured by nanoindentation method. The adhesion of coatings to the branches was determined by the shear on the tensile testing machine RPM-10MG4. It has been determined that mechanical polishing of the p-type semiconductor branches based on Bi2Te3−Sb2Te3 solid solution results in surface hardening, and also increases the adhe sion of the Mo–Ni switching barrier layers by a factor of 2 compared with the adhesion of Mo–Ni layers on the surface of untreated branches. Subsequent electrochemical polishing increases the adhesion of Mo–Ni layers by 1.3 times, and pulsed photon treatment by 1.4 times compared with mechanically polished branches. It is shown that the energy effect of an PPT stimulates local recrystallization of the defective layer near the surface of semiconductor branches at a depth of 100−200 nm and increases the hardness of the near-surface layers of the Bi2Te3− Sb2Te3 solid solution by 1.2 times.

Abstract. The narrow band gap lead chalcogenide semiconductors and related solid solutions are capable to detect effectively an infrared (IR) radiation in the wavelength range 3–25 μm. Due to the unique combination of the optimal dielectric permittivity, Seebeck coeffi cient, and high thermal conductivity, lead telluride is promising material for manufacturing of high-performance intermediate-temperature thermoelectric devices. By scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray analysis (XRD), and atomic force microscopy (AFM) the quantitative elemental composition, phase nature, surface morphology, and average surface roughness of homogeneous lead telluride fi lms synthesized by modifi ed «hot wall» technique on Si (100) substrates have been studied. The XRD patterns have shown that at condition of high condensation process rate, which was realized at substrate temperatures below T = 573 K and corresponded to the maximum deviation from the thermodynamic equilibrium, polycrystalline PdTe fi lms on Si (100) substrates were synthesized only. The increase in temperature Si (100) substrate to T = 593-613 K has led to fabrication of mosaic single-crystal PdTe fi lms with (100) texture. By SEM and AFM methods it has been found that under constant values of lead and tellurium vapour pressure synthesis an increase in the Si substrate temperature led to increase in crystallite average lateral dimension of PbTe fi lm on Si (100) substrates. By AFM method it has established the tendency of the average surface roughness value increasing with average thickness for both polycrystalline and mosaic single crystal PbTe/Si (100) fi lms. At the same average thickness values polycrystalline PbTe/Si (100) fi lms are characterized by higher surface roughness compared to mosaic single-crystal PbTe (100) samples. It is suggested that of average surface roughness-to-fi lm thickness ratio it can be used as a criterion of evaluation of surface contribution to functional properties of PbTe fi lms. It has been shown that with optimum values of average roughness-to-thickness ratio mosaic single-crystal PdTe (100) fi lms with thickness over 1.2 μm are characterized.