Structural, electrical and optical characterization of bismuth telluride and antimony telluride thin films deposited by pulsed laser deposition

Bismuth Telluride (Bi2Te3) and Antimony Telluride (Sb2Te3) are the most used thermoelectric materials near room temperature applications. Even though few attempts have been made to deposit Bismuth telluride using pulse laser deposition (PLD), not many have used it to deposit Antimony Telluride thin films. In this thesis, both Bismuth Telluride and Antimony Telluride thin films were deposited using PLD on n-type Silicon substrate in Argon (Ar) atmosphere at substrate temperatures ranging from 25°C to 450°C. The surface morphology of both the films was studied using Atomic force microscopy (AFM) and their crystalline properties were studied using X-ray diffraction (XRD) analysis. The effect of substrate temperature on the surface morphology and crystallinity of the films was investigated. The surfaces properties such as average surface height, RMS deviation and Peak surface height of both Bi2Te3 and Sb2Te 3thin films. X-ray diffraction confirms the hexagonal lattice structure of both the deposited materials. XRD results also show that all the films are polycrystalline and have a specific preferred orientation at higher substrate temperatures. The grain sizes of all the films are calculated using Scherrer formula and plotted as a function of temperature for both the materials.;The electrical properties of the films were characterized by impedance spectroscopy and the sheet resistance was measured using four point probe equipment. From the impedance spectroscopy, Nyquist plots were obtained for all the films. From these plots, an equivalent circuit model was developed to fit the experimental data. The values of the circuit parameters were calculated from the Nyquist plots for all the films and are plotted against the temperature. It was found that the values of series resistance are consistent with the values of the sheet resistance obtained from four point probe. Both parameters are plotted against the temperature for comparison. The results provided us with the understanding of the grain boundary and the junction between the materials.;The materials were also deposited on microscopic glass slides at 150°C using the same PLD technique to study the optical properties using ultra violet-visible (UV-Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopic measurements. Using UV-Vis spectroscopy, the absorbance spectra of all deposited films was studied. The films deposited on the glass slides were compared with those deposited at 150°C on Si. It was found from the comparison that the Si substrate has almost negligible effect on the absorbance spectra of the Bi2Te3 films whereas it increases the absorbance of Sb2Te3films. Using FTIR spectroscopy, the transmission spectra of the deposited films deposited was studied, including those deposited on the glass slides. No absorption peaks corresponding to the deposited films were observed as the peaks corresponding to the deposited films occur at lower frequency which is not in the range of our experiment. It was also observed that the films deposited on glass had some additional peaks than on Si due to Si impurities. The optical band gaps for both the deposited materials were also obtained from the Tauc plots.