SURFACE MORPHOLOGY OF PbTe/Si (100) FILMS SYNTHESIZED BY MODIFIED "HOT WALL" EPITAXY TECHNIQUE

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 coefficient, 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 films synthesized by modified «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 films 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 films 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 film 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) films. At the same average thickness values polycrystalline PbTe/Si (100) films are characterized by higher surface roughness compared to mosaic single-crystal PbTe (100) samples. It is suggested that of average surface roughness-to-film thickness ratio it can be used as a criterion of evaluation of surface contribution to functional properties of PbTe films.  It has been shown that with optimum values of average roughness-to-thickness ratio mosaic single-crystal PdTe (100) films with thickness over 1.2 μm are characterized.

ACKNOWLEDGEMENTS

The research was carried out using the equipment of the Centre for Collective Use of Scientific Equipment of Voronezh State University.