S. Selvaraj

Bio: S. Selvaraj is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Thin film & Electrical resistivity and conductivity. The author has an hindex of 3, co-authored 5 publications receiving 36 citations.

Thickness and temperature dependence of electrical properties of Bi2(Te0.1Se0.9)3 thin films

Abstract: Thin films of different thicknesses have been vacuum deposited onto clean glass plates held at room temperature using the flash evaporation technique in a vacuum of 2×10−5 Torr. The structural characterization of the bulk and the thin films was carried out using x-ray diffraction, transmission electron microscopy, and selected area electron diffraction techniques. Electrical resistance and thermoelectric power of the films were measured in the same vacuum of 2×10−5 Torr in the temperature range 300–450 K. The conduction activation energy of the films was calculated using the electrical resistivity and thermoelectric power data of the films. The thickness dependence of the activation energy observed is attributed to the polycrystalline nature of the films. Grain growth and reorientation of the grains take place during the annealing process. The thickness dependence of electrical resistivity and thermoelectric power of the films are explained by the effective mean free path model [C. R. Tellier, Thin Solid ...

Size and temperature dependence of electrical resistance and thermoelectric power of bi2te2se1 thin films

Abstract: Thin films of Bi2Te2Se1 of various thicknesses have been deposited on clean glass plates using the flash evaporation technique. Electrical resistance and thermoelectric power measurements have been carried out on these films in the temperature range 300–485 K. The thickness dependences of electrical resistivity and thermoelectric power of the films have been analyzed using the effective mean-free path model. The thickness dependence of activation energy of the films is explained by Seto’s polycrystalline model. Various material parameters such as mean-free path and Fermi energy have been calculated from the analysis of experimental data. The thermoelectric power factor of the films has been calculated using the measured electrical resistivity and thermoelectric power values.

Electrical conduction mechanisms in thermally evaporated tungsten trioxide(WO3) thin films

Abstract: Thin films of amorphous tungsten trioxide, a-WO3, have been thermally evaporated onto glass substrate held at 350K. Annealing at 723K caused the formation of polycrystalline tungsten trioxide, c-WO3, with a monoclinic structure. The dark DC electrical conductivity of both a-WO 3 and c-WO3 was studied over a temperature range from 298 to 625K in two environmental conditions (air and vacuum). A simple Arrhenius law, a polaron model and a variable range hopping model have been used to explain the conduction mechanism for a-WO3 films. Using the variable range hopping model, the density of localized states at the Fermi level, N(EF), was found to be 1.08 × 1019eV -1cm-3. The mechanism of electrical conduction in c-WO3 films is explained by means of the Seto model. The Seto model parameters were determined as the energy barrier (Eb ≤ 0.15eV), the energy of trapping states with respect to the Fermi level (Et ≤ 0.9eV) and the impurity concentration (ND ≤ 4.05 × 1015eV-1cm-3). The thickness dependence of resistivity of c-WO3 films has been found to decrease markedly with increasing film thickness, which is explained on the basis of the effective mean free path model. Using this model, the mean free path of electrons in c-WO 3 films was evaluated. The temperature dependence of the thermoelectric power for a-WO3 films reveals that our samples are n-type semiconductors.

Determining the Thermal Conductivity of Nanocrystalline Bismuth Telluride Thin Films Using the Differential 3 ω Method While Accounting for Thermal Contact Resistance

Abstract: We have estimated the thermal conductivity of nanocrystalline bismuth telluride thin films using the differential 3ω method, taking into account the thermal contact resistance (TCR) between the substrate and thin-film layers. The thin films were prepared on alumina substrates by radio-frequency (RF) magnetron sputtering at temperature of 200°C. Film thickness varied between 0.8 μm and 3.1 μm. The structural properties of the films were analyzed using x-ray diffraction analysis. Their electrical conductivity, Seebeck coefficient, and power factor were evaluated. For measurement of thermal properties by the differential 3ω method, SiO2 thin films were deposited onto the samples, to act as insulating layers. Thin aluminum wire was then patterned onto the SiO2 layer. The observed variations in temperature amplitude as a function of film thickness indicated that the TCR contribution was very small and could therefore be neglected when estimating the thermal conductivity of the thin films. The thermal conductivity of the nanocrystalline bismuth telluride thin films with thickness of 0.8 μm and 2.1 μm were determined to be 0.55 W/(m K) and 0.48 W/(m K), respectively.

Thermoelectric Characteristics of the Thermopile Sensors with Variations of the Width and the Thickness of the Electrodeposited Bismuth-Telluride and Antimony-Telluride Thin Films

Abstract: Thermopile sensors were processed on glass substrates by using successive electrodeposition of p-type Sb-Te and n-type Bi-Te thin films, and their thermoelectric characteristics were measured. The thermopile sensor, consisting of the p-n legs of 2 μm-thickness and 50 μm-width, exhibited the sensitivity of 24.8 mV/K. By changing the width of the p-n thin-film legs from 50 to 100 μm, the sensitivity decreased to 15.4 mV/K because of less pairs of the p-n thin-film legs in the thermopile. With increasing the thickness of the thin-film legs from 2 to 5 μm, the sensitivity was improved to 36.5 mV/K due to higher Seebeck coefficients of the 5 μm-thick Bi-Te and Sb-Te films than those of the 2 μm-thick films.