Showing papers on "Antimony telluride published in 2001"

Preparation and characterization of p-type Sb2Te3 and n-type Bi2Te3 thin films grown by coevaporation

Abstract: p-type antimony telluride thin films and n-type bismuth telluride thin films have been deposited by coevaporation on glass substrates. The conditions for deposition have been investigated as a function of substrate temperature (Ts), flux ratio (Fr=F(Te)/F(Sb, Bi)) and optimized to achieve a high thermoelectric power factor. The quality of deposited films, e.g. structure, composition and morphology, has been examined by x-ray diffraction, energy dispersive x-ray analysis, flame atomic absorption spectroscopy, and with an atomic force microscope. The thermoelectric properties of the thin films have been evaluated by room temperature measurement of the Seebeck coefficient, Hall coefficient, and electrical resistivity. Both the crystallinity and the transport properties are strongly affected by nonstoichiometry with the highly stoichiometric samples exhibiting a high crystallinity and high thermoelectric power factor. The Seebeck coefficient and electrical conductivity of p-type Sb2Te3 thin film (αp, σp) and ...

In-situ monitoring of the growth of Bi 2 Te 3 and Sb 2 Te 3 films and Bi 2 Te 3 -Sb 2 Te 3 superlattice using spectroscopic ellipsometry

Abstract: In this work, we present in-situ monitoring of the growth of bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thin films as well as Bi2 Te3-Sb2Te3 superlattice using a spectroscopic ellipsometer (SE). Bi2Te3 and Sb2 Te3 films were grown by metalorganic chemical vapor deposition (MOCVD) at 350 C. A44-wavelength ellipsometer with spectral range from 404 nm to 740 nm was used in this work. The optical constants of Bi2 Te3 and Sb2Te3 at growth temperature were determined by fitting a model to the extracted in-situ SE data of optically thick Bi2 Te3 and Sb2 Te3 films. Compared to the optical constants of Bi2 Te3 and Sb2 Te3 at room temperature, significant temperature dependence was observed. Using their optical constants at growth temperature, the in-situ growth of Bi2 Te3 and Sb2 Te3 thin films were modeled and excellent fit between the experimental data and data generated from the best-fit model was obtained. In-situ growth of different Bi2 Te3-Sb2 Te3 superlattices was also monitored and modeled. The growth of Bi2 Te3 and Sb2 Te3 layers can be seen clearly in in-situ SE data. Modeling of in-situ superlattice growth shows perfect superlattice growth with an abrupt interface between the two constituent films.

Structural Defects in Tin-Doped Antimony Telluride Single Crystals

Abstract: The structural perfection and homogeneity of Czochralski-grown Sb2Te3and Sb1.96Sn0.04Te3crystals were characterized by transmission electron microscopy and electron probe x-ray microanalysis. The Sb, Sn, and Te core-level and valence-band x-ray photoelectron spectra were measured, and the corresponding binding energies were determined. The effect of Sn doping on the electronic structure and transport properties of the crystals was examined. The crystals were shown to be uniform in Sb : Te ratio and to have a relatively perfect structure. The dislocation density in the crystals was determined by electron microscopy and selective etching. The origin of the moire patterns observed in electron micrographs was discussed. Sn doping of Sb2Te3was shown to produce no significant shifts of the core levels or changes in the electronic density of states in the valence band.

Fabrication of a p-type Sb/sub 2/Te/sub 3/ and n-type Bi/sub 2/Te/sub 3/ thin film thermocouple

Abstract: A thin film Sb/sub 2/Te/sub 3/-Bi/sub 2/Te/sub 3/ based thermocouple was fabricated. P-type antimony telluride thin films and n-type bismuth telluride thin films have been deposited by co-evaporation on to glass substrates. The conditions for deposition have been investigated as a function of substrate temperature (T/sub s/) and flux ratio (F/sub r/ = F(Te)/F(Sb,Bi)) and optimised to achieve a high thermoelectric power factor. The qualities of deposited films, e.g. structure, composition and morphology, have been examined by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDXA), flame atomic absorption spectroscopy (FAAS) and atomic force microscope (AFM). The thermoelectric properties of the thin films have been studied by room temperature measurement of the Seebeck coefficient, Hall coefficient and electrical resistivity. It has been observed that the Seebeck coefficient and electrical conductivity of p-type Sb/sub 2/Te/sub 3/ thin film (/spl alpha//sub p/, /spl sigma//sub p/) and n-type Bi/sub 2/Te/sub 3/ thin films (/spl alpha//sub n/, /spl sigma//sub n/) were found to be about 185 /spl mu/V/K, 0.32 /spl times/ 10/sup 3/ /spl Omega//sup -1/ cm/sup -1/ and -228 /spl mu/V/K, 0.77 /spl times/ 10/sup 3/ /spl Omega//sup -1/ cm/sup -1/, respectively. From optimal deposition parameters, a thin film thermocouple was fabricated and operated in Peltier mode. The observed maximum value for temperature difference between hot and cold end is about 15 K for a current of 50 mA. The results indicate that good quality antimony telluride and bismuth telluride thin films grown by co-evaporation are promising candidates for use in a micro-Peltier module.

Sb K-edge absorption fine structure of Sb2Te3.

Abstract: In order to study the local structure of some antimony compounds, Sb K-edge XAFS spectra were measured for Sb2Te3 and InSb. The measurements were performed in the transmission mode at BL-01 of SPring-8. Though crystal structure of antimony telluride Sb2Te3 is known by X-ray diffraction analysis, the EXAFS analyses give controversial result on the Sb-Te distance and the coordination number of Sb2Te3. Comparing the observed XANES spectra for Sb2Te3 with FEFF8 calculation, we can explain the controversial results which are also supported by the observed X-ray powder diffraction.