In situ electrical conductivity and amorphous-crystalline transition in vacuum-deposited thin films of Se20Te80 alloy
01 Jul 1987-Journal of Materials Science (Kluwer Academic Publishers)-Vol. 23, Iss: 11, pp 3869-3875
TL;DR: In this article, the electrical conductivity of thin films of Se80Te20 polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied during in situ heating and cooling cycles.
Abstract: The electrical conductivity of thin films of Se80Te20 polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied duringin situ heating and cooling cycles. From the electron diffraction of as-grown films it is seen that the studied films are amorphous at room temperature. The electrical conductivity and electron diffraction studies showed that the as-grown amorphous thin films undergo an amorphous-crystalline transition in the temperature range 340 to 360 K. Upon cooling, the films appear to undergo a crystalline crystalline transition around the same temperatures. There does not appear to be any dependence of the amorphous-crystalline transition temperature on the thickness of the films. However, high-resistance films (thinner films) have a well-defined transition temperature while the low-resistance films (thicker films) have a broader transition. The electrical conductivity of polycrystalline Se80Te20 films above 360 K appears to be an exponential function of reciprocal temperature.
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TL;DR: In this paper, the activation energy of crystallization and Avrami index were obtained for one-and two-dimensional growth in the Se70Te30 thin films, respectively.
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TL;DR: In this paper, a comparison of the electrical parameters in amorphous chalcogenide, obtained using three different methods (electrical impedance, d.c. and the four-point resistivity measurements), has shown that impedance measurement is the most appropriate because it is able to separate the contributions of the bulk and contacts.
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TL;DR: In this paper, it was found that the thermoelectric power of these films is slightly different during the heating and cooling cycles which is attributed to slight reorientation of microcrystallites as also evidenced by x-ray diffraction.
Abstract: Thin films of different thicknesses in the range 400–1600 A have been vacuum deposited on clean glass substrates held at room temperature by very fast evaporation of the Se10Sb10Te80 bulk alloy. The thermoelectric power of these films has been measured as a function of temperature during heating and cooling cycles by the integral method. It is found that the thermoelectric power of these films is slightly different during the heating and the cooling cycles which is ascribed to slight reorientation of microcrystallites as also evidenced by x‐ray diffraction. It is further found that the thermoelectric power (at a constant temperature) is a function of film thickness; it varies nearly linearly with reciprocal thickness. From these data, the nature of carrier scattering in the films has been ascertained. From the energy‐dispersive x‐ray analysis patterns of the films the semiquantitative content of the constituent elements Sb, Se, and Te has been determined.
7 citations
TL;DR: In this article, Pichard et al. measured the thermoelectric power of thin films of the alloy Se20Te80 of different thicknesses between 600 and 1250 A on clean glass substrates at room temperature in a vacuum of 5 × 10-5 Torr by the vacuum deposition technique.
2 citations
TL;DR: In this article, optical absorption, energy band gap and X-ray structural analysis of Se85 Te15 and Se85 As15 films are reported, and the effect of annealing on these parameters has also been indicated.
Abstract: Amorphous selenium alloy films have been found to exhibit excellent photosensitive properties from 300 to 700 nm. These films constitute the essential part of xerographic photoreceptors. Optical absorption, energy band gap and X-ray structural analysis of Se85 Te15 and Se85 As15 films are reported. The effect of annealing on these parameters has also been indicated.
1 citations
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TL;DR: In this paper, the variation of cell dimensions with composition departs only slightly from linearity: c shows a certain tendency to contraction (this corresponds to a smaller valency angle in the chains of atoms than is required by a linear variation): a varies much less (2 percent between Se and Te) and in a manner which depends upon the preparation of the alloy, as already observed for pure selenium by H. Krebs.
Abstract: Tellurium and metallic (hexagonal) selenium were shown to give solid solution in any concentration. The variation of the cell dimensions with composition departs only slightly from linearity: c shows a certain tendency to contraction (this corresponds to a smaller valency angle in the chains of atoms than is required by a linear variation): a varies much less (2 percent between Se and Te) and in a manner which depends upon the preparation of the alloy (as already observed for pure selenium by H. Krebs).The presence of sharp (hk·l) lines with l≠0 in all the alloys suggests that these must be composed not of homogeneous chains (i.e., Se chains, Te chains packed together), but of composite chains, in which the homogeneous sequences must be fairly short.
97 citations
TL;DR: In this article, the compositional dependence of some physical properties such as: density, dc conductivity and thermal conductivity, have been investigated and the effects of composition, temperature and time of annealing are explained in terms of structural changes and crystallization kinetics.
Abstract: This paper reviews some work done in our laboratory on the binary amorphous system Se−Te. The compositional dependence of some physical properties such as: density, dc conductivity and thermal conductivity, have been investigated. A number of results are reviewd. The effects of composition, temperature and time of annealing on the dc conductivity are explained in terms of structural changes and crystallization kinetics. The spectrum of the activation energies of crystallization for the amorphous solid and liquid phases is discussed.
42 citations
TL;DR: The optical and electrical properties of selenium-tellurium alloys have been studied in this paper, where the authors found that the bandgap of disordered evaporated layers of the alloys Se3Te and SeTe have been estimated to be 1.87 and 1.58 eV, respectively, from the break from the approximately exponential absorption edge.
Abstract: The optical and electrical properties of selenium‐tellurium alloys have been studied. These properties depend upon the degree of order of the alloys. The bandgap of disordered evaporated layers of the alloys Se3Te and SeTe have been estimated to be 1.87 and 1.58 eV, respectively, from the break from the approximately exponential absorption edge. This is consistent with a linear variation of bandgap with composition. From the dispersion of the refractive index, another characteristic frequency larger than the bandgap is found. The disordered layers convert to a crystalline form when heated above room temperature. The conversion process has been followed by observing the change of resistivity of the layers with time. During much of the conversion, this change is approximately exponential. The time constant in this region has an exponential temperature dependence, being characterized by activation energies of 1.4 and 0.8 eV for Se3Te and SeTe, respectively. The rate of conversion of the alloys increases with increasing tellurium content. As with selenium, the ordered alloys are more conducting than the disordered alloys and the absorption in the low photon energy region is greater. An absorption band has been found in the ordered alloys which is associated with transitions between tellurium levels. The strength of the band is directly proportional to the tellurium concentration; the energy of separation of the levels, which is a reflection of the local crystal field, varies linearly with the composition of the alloys.
40 citations
TL;DR: In this article, conductivity measurements have been made as a function of temperature and electric field in bulk amorphous Se, Se-Te, SeSb, and SeTe-Ge, to identify the conduction mechanism and to study the effect of various dopants in Se on the conductivity.
Abstract: dc conductivity measurements have been made as a function of temperature and electric field in bulk amorphous Se, Se-Te, Se-Sb, and Se-Te-Ge, in order to identify the conduction mechanism and to study the effect of various dopants in Se on the conductivity. It is found that the conduction in all the samples, except in Se-Te-Ge, is through the tail of the localized states via thermally activated tunneling. In the Se-Te-Ge system, the conduction in the high-temperature region is through the extended states and in the low-temperature region via thermally activated tunneling in the localized states. It is found that the electric field effect is to increase the conductivity and to decrease the activation energy. An empirical model has been suggested to explain these results.
34 citations