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Journal ArticleDOI

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

01 Sep 1983-Journal of Applied Physics (AIP Publishing)-Vol. 54, Iss: 9, pp 5252-5255
TL;DR: In this paper, the electrical resistance of Ag2Te films has been measured as a function of temperature during heating, which was carried out immediately after the film formation, and 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.
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.
Citations
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Journal ArticleDOI
TL;DR: In this article, a solution-phase synthesis of silver telluride and bismuth-telluride nanowire heterostructure using tellurium (Te) nanowires as sacrificial template and site-selective conversion strategy is reported.
Abstract: In this paper, we report a solution-phase synthesis of silver telluride and bismuth telluride nanowire heterostructure using tellurium (Te) nanowire as sacrificial template and site-selective conversion strategy. High-resolution transmission electron microscope studies confirm sharp interface with possible epitaxial growth between silver telluride and bismuth telluride regions. Through tuning the precursor amount (bismuth and silver precursors) during the reaction, the composition between silver telluride and bismuth telluride can be adjusted. Moreover, the mass produced powder of nanowire heterostructure is consolidated into nanocomposite pellets, and thermoelectric properties of the nanocomposite pellets are investigated between 300 and 400 K. Results show that our materials are p-type with reduced lattice thermal conductivity and a ZT of ∼0.41 at 400 K, which is the best reported value for p-type silver telluride.

51 citations

Journal ArticleDOI
TL;DR: In this article, Das and Karunakaran showed that the phase transition temperature of thin films is a function of thickness increasing with a decrease in the thickness of the thin films.
Abstract: Thin films of silver selenide (Ag2Se) between thicknesses of about 700 and 2200 A have been prepared on glass substrates at room temperature in a vacuum of 5×10−5 Torr. After vacuum annealing the films (at about 373 K for 3 h) electrical resistivity measurements on these films have been carried out in vacuum. From the increase in the rate of decrease of resistance with temperature, the phase transition temperatures (orthorhombic to body‐centered cubic) of the different films have been located. It is found that the phase transition temperature of the thin films is a function of thickness increasing with a decrease in the thickness. This observation has been explained by a recently developed theory [V. Damodara Das and D. Karunakaran, J. Phys. Chem Solids 46, 551 (1985)] of phase transitions in thin films modified further. Also, an order‐of‐magnitude value of the difference in the function of specific surface and interfacial energies of the two phases has also been determined using the theory.

38 citations

Journal ArticleDOI
TL;DR: In this article, it was observed from the studies of electrical resistivity of films of SnSe of different thicknesses and substrate temperatures that resistivity decreases with increase in thickness and substrate temperature.
Abstract: It is observed from the studies of electrical resistivity of films of SnSe of different thicknesses and substrate temperatures that resistivity decreases with increase in thickness and substrate temperature. The study of variation in band gap with thickness shows a linear relationship between band gap and 1/t2. Finally, band gap – substrate temperature studies show that the band gap increases with substrate temperature.

27 citations

Journal ArticleDOI
TL;DR: In this article, the dependence of substrate conditions and the effective thickness of MoO3 films on the morphology of nanostructures and their structural aspects were reported, and the electron microscopy measurements show that the length and the aspect ratio of Nanobibbons increased by 260% without any significant change in the width for a change in effective thickness from 5´nm to 30´nm.

25 citations

References
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Book
01 Jan 1969

2,189 citations

Book
01 Jan 1971

238 citations

Journal ArticleDOI
TL;DR: In this paper, the barrier theory of the infrared photoconductivity of PbS films is discussed, according to which the high resistance of the films arises from $n √ √ n √ ϵ barrier at the surfaces between the crystallites forming the films, the barriers being formed in the oxidizing process used in preparing the films.
Abstract: The barrier theory of the infrared photoconductivity of PbS films is discussed, according to which the high resistance of the films arises from $n\ensuremath{-}p\ensuremath{-}n$ barriers at the surfaces between the crystallites forming the films, the barriers being formed in the oxidizing process used in preparing the films. Under the action of light, electron hole pairs are formed, these carriers become trapped in the $n$- and $p$-type regions, respectively, the resulting charge density lowers the barriers, and hence the conductivity is increased. This theory is worked out quantitatively, and compared with experimental results of Mahlman on films of the type actually used as sensitive photoconductors. The theory shows good qualitative and quantitative agreement with experiment in numerous respects, including the explanation of the dark conductivity of the films and its dependence on temperature, the photoconductivity as a function of irradiance and temperature, the time constants involved in the rise or decay of the photoconductivity, and the short-wave limit of the photoconductivity. In working out the theory of the barrier model, we use the properties of the bulk material as determined by Petritz and Scanlon, and the properties of the films are found to be consistent with our knowledge of the behavior of the bulk material.

157 citations

Journal ArticleDOI
TL;DR: In this paper, the Seebeck coefficient α, electrical conductivity σ, and thermal conductivity K data are given for a number of Ag2Te specimens measured at room temperature, and the maximum value observed for the figure of merit α2σ/K was 1.3×10−3°C−1.
Abstract: The Seebeck coefficient α, electrical conductivity σ, and thermal conductivity K data are given for a number of Ag2Te specimens measured at room temperature. The maximum value observed for the figure of merit α2σ/K was 1.3×10−3°C−1. The relationship between K and σ was linear, and Kel could be expressed approximately by (π2/3) (k/e)2σT. Kph was found to be 0.72×10−2 w cm−1°C−1. There was no evidence of an ambipolar diffusion contribution to K. It is suggested that the small energy gap (0.02 ev) previously determined in this compound could account for the absence of a measurable ambipolar diffusion effect, the degeneracylike behavior of Kel, and the relatively low values of the Seebeck coefficient.

75 citations

Journal ArticleDOI
TL;DR: In this paper, the Hall coefficient, resistivity, and Seebeck coefficient of $n$-and $p$-type specimens of Ag2Te have been measured over the temperature range from 55 to 300.
Abstract: The Hall coefficient, resistivity, and Seebeck coefficient of $n$- and $p$-type specimens of ${\mathrm{Ag}}_{2}$Te have been measured over the temperature range from 55 to 300\ifmmode^\circ\else\textdegree\fi{}K. These results indicate that the compound is highly degenerate over the whole temperature range studied. Calculations were made of the effective masses, mobility ratios, and energy gap and gave order of magnitude values.

45 citations