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

Abstract

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.

Keywords

• lead telluride
• thin fi lms
• microstructure
• surface morphology
• crystallite average lateral dimension
• surface roughness.