V. Damodara Das

Bio: V. Damodara Das is an academic researcher. The author has contributed to research in topics: Bismuth & Thin film. The author has an hindex of 2, co-authored 2 publications receiving 14 citations.

Semiconducting behavior in antimony-doped bismuth films

Abstract: The electric resistivity and Hall effect were studied for the vacuum evaporated and annealed ∠1 at.% Sb‐doped bismuth alloy films of various thickness (350–3500 A) in the temperature range of 77–510 K. Contrary to the behavior of bulk BiSb alloy, where the alloy becomes semiconducting only at about 4 at.% of Sb and above (A.L. Jain, 1959), it is found that thin films of 1% Sb‐doped Bi alloy are semiconducting. Moreover, this semiconducting trend begins at about room temperature unlike in bulk BiSb alloys where it is observed only at temperatures below about 180 K. The present type of behavior has been predicted and observed by some earlier workers (Ivanov et al. 1963, 1964). The intercrystalline barrier activation energies determined for various film thicknesses deposited at different substrate temperatures (257 K, 300 K, 373 K) were found to vary with thickness and substrate temperature, activation energy decreasing with increasing thickness and substrate temperature. These observations have been attribu...

Effect of substrate temperature during growth on defect density in bismuth thin films

Abstract: Bismuth thin films of thickness 720±10 A have been vacuum deposited on clean glass substrates held at various substrate temperatures ranging between 30 ° and 185 °C at a constant deposition rate 0f 3±0.3 A s. Immediately after the formation of the films, the heat treatment was given to the films in situ. For each film, the resistance was recorded as a function of temperature during the heat treatment. It has been found that the resistance of the films decreases when the temperature increases during the first cycle of heating, and this has been attributed to the removal of defects. During the first cycle of cooling and the next cycle of heating and cooling, it is observed that the resistance first decreases when the temperature increases and then increases as the temperature increases. Using Vand’s theory, from the resistance–temperature data during heat treatment, both defect density and the initial lattice distortion energy spectra have been evaluated. It is observed from these spectra that as the substr...

Semiconducting behavior of Ag2Te thin films and the dependence of band gap on thickness

Abstract: Thin films of Ag2Te of various thicknesses in the range 500–1500 A have been prepared by thermal evaporation of the compound under vacuum on clean glass substrates held at room temperature. The electrical resistance of the films has been measured as a function of temperature during heating, which was carried out immediately after the film formation. The observed exponential decrease of resistance with temperature up to the transition point points to the semiconducting nature of the low temperature polymorph of Ag2Te. The band gap of the low temperature phase is calculated for various thicknesses of the films and it is found that the band gap is a function of film thickness, increasing with decreasing thickness. The increase in the band gap, which was found to be inversely proportional to the square of the film thickness, is attributed to quantization of electron momentum component normal to film plane.

Quantum freeze‐out effect in a size‐limited intrinsic transport

Abstract: The size‐limited resistivity of intrinsic thin films is calculated theoretically in the size‐quantum limit (SQL), where the film thickness d is comparable to the de Broglie wavelength λD of the electrons (λD≥d). The variation of the intrinsic carrier concentration with the film thickness is taken into account. We find that in the SQL, the ratio of the thin film resistivity to the bulk resistivity increases exponentially with decreasing film thickness. This arises because of the increase in the effective band gap of an intrinsic thin film with film thickness as a result of size quantization.

Ion beam mixing to produce Bi/Sb alloys for thin film thermoelectric devices

Abstract: Ion beam mixing using 80 keV Ar+ and 120 keV Kr+ has been used to produce thin films of BiSb with various compositions of Sb ranging from 5% to 49%. In addition, n- and p-type doping of the films was attempted by the addition of Se and Sn during the mixing process. Rutherford backscattering analysis indicated that uniform composition films were formed after doses of 1.5–3 × 1016 Ar+cm−2and 7 × 1015 Kr+cm−2. TEM measurements show that grain growth occurs during the mixing. Thermo-electric measurements indicate that the Seebeck coefficient, S, has a maximum value of 66 μ V K . for an Sb concentration of 13%. This alloy also exhibits a 30% increase in the figure of merit over that of a pure Bi film. Attempts to dope the BiSb films using Sn and Se resulted in no change in S but an increase of 35% in the Seebeck voltage, Vs.