Showing papers by "V. Damodara Das published in 1996"

Optical and electrical investigations of indium oxide thin films prepared by thermal oxidation of indium thin films

Abstract: Indium oxide thin films have been prepared by thermal oxidation of vacuum‐deposited indium thin films in air in an open furnace at about 600 K. These indium oxide thin films prepared by thermal oxidation have been examined for optical transparency by measuring their optical absorbance as a function of wavelength. From the optical absorption data, optical band gap and the nature of the forbidden energy gap in the indium oxide thin films have been determined. Electrical conductivity measurements have also been carried out on the above oxide films as a function of temperature during heating and cooling cycles in vacuum. It is found that after the first heating, electrical conductivity increases to a significant extent due to removal of point defect clusters due to annealing which contribute to both carrier generation and scattering. From the thermoelectric power measurements carried out, it has been concluded that electrons are the majority carriers in these indium oxide thin films.

Thickness and temperature effects on thermoelectric properties of Pb0.6Sn0.4Te thin films

Abstract: Electrical resistivity and thermoelectric power measurements have been carried out as a function of thickness in the temperature range 300–480 K on flash evaporated Pb0.6Sn0.4Te thin films. Electrical resistivity and thermoelectric power variation with temperature of the films suggests that they have a near‐degenerate semiconductor behavior. The effective mean‐free‐path model of classical size effect has been used to analyze the thickness dependence of resistivity and thermoelectric power. Both are found to be near‐linear functions of inverse thickness. From the analysis of the experimental data, material parameters like mean free path and Fermi energy have been evaluated. Thermoelectric figure of merit has been calculated using the measured values of thermoelectric power and electrical resistivity and by taking thermal conductivity data from the literature. Thermoelectric figure of merit is also found to be thickness and temperature dependent.

Electron Microscopic Studies and Microchemical Analysis of Se 10Sb 10Te 80 Ternary Alloy Thin Films

Abstract: Thin Films of thicknesses less than 1000 A have been deposited in a vacuum of 5 ×10-5 Torr by the very fast evaporation (~50 A/s) of the ternary Se10Sb10Te80 bulk alloy pieces onto cleaned glass plates which were held at room temperature vertically above the evaporation source (at a distance of 25 cm) From the energy dispersive X-ray analysis (EDAX) patterns of the films, the presence of Te, Sb and Se has been confirmed and the semi-quantitative content of the constituent elements in the alloy films has been determined Film specimens for transmission electron microscopy have been detached from these glass substrates by dippping the latter in very dilute HF solution These film specimens have been examined in an electron microscope Electron diffraction patterns reveal that the films are not amorphous but are polycrystalline in most of the regions, but also single crystalline in some regions which have a darker contrast in bright field transmission electron micrographs Analysis of the single crystalline (spot) patterns obtained reveals that the single crystalline microcrystallites in different regions are oriented differently The orientations of these microcrystallites have been determined

Effect of oxygen adsorption on the electrical resistance of thin films

Abstract: Thin films of of varying thicknesses deposited by the flash evaporation method showed considerable change in resistance with time when exposed to oxygen or atmosphere. The change in resistance is found to decrease with increase in thickness and with increase in substrate temperature. The observed behaviour is explained by an oxygen adsorption model, which is further supported by the x-ray photoelectron spectroscopy (XPS) of the films.