Electrical conductivity of air-exposed and unexposed lead telluride thin films-temperature and size effects
TL;DR: In this paper, it was found that the electrical resistivity of the air-exposed films is much higher than that of the as-grown (unexposed) thin films.
Abstract: Thin films of PbTe of different thicknesses have been prepared on glass substrates at room temperature by vacuum deposition. It is found that the electrical resistivity of the air-exposed films is much higher (by about 2 to 3 orders of magnitude) than that of the as-grown (unexposed) thin films. The electrical resistivity temperature behaviours of both the air-exposed and as-grown (unexposed) thin films of PbTe are different but both show hysteresis behaviour during successive heating-cooling cycles. These observations can be explained by considering that the desorption of absorbed gas molecules (mainly oxygen) and creation of defects at higher temperatures during heating influence the electrical conduction. Further, the time factor involved in gas desorption-adsorption can cause the observed hysteresis in temperature-dependent conduction behaviour. The as-grown (unexposed) thin-film conductivity exhibits the expected reciprocal thickness dependence due to the thickness effect, but the air-exposed film conductivity does not. This can be explained to be due to the complete masking of the thickness effect by the gas adsorption effect in air-exposed film conductivity. The reciprocal thickness dependence observed in the case of unexposed film conductivity has been explained by the 'effective mean free path' model. The low value of the 'grain boundary' mean free path obtained by the analysis points to the fact that in polycrystalline films, grain boundary scattering is extensive and controls the film conductivity.
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TL;DR: In this article, a thin film p-cadmium telluride has been electrodeposited from non-aqueous propylene carbonate, and the resistivity of the resultant film was determined by either two or four-strip methods, depending on the resistance of the film.
Abstract: Thin film p-cadmium telluride that has been electrodeposited from non-aqueous propylene carbonate has been doped with copper using two electrochemical methods. The first involved electrochemical codeposition (in situ doping) of copper and cadmium telluride, and the second employed electromigration of copper into thin film cadmium telluride that had been annealed. After the film was removed from the conductive substrate, the resistivity of the resultant film was determined by either two- or four-strip methods, depending on the resistance of the film. To avoid current leakage by way of surface moisture, the film resistivity was measured under vacuum. The temperature dependence of the resistivity was determined for both doped and undoped films, and activation energies were obtained. As the copper density was increased, the resistivity and activation energy decreased. A Hall effect measurement of highly doped film revealed that the carrier density is substantially less than the estimated copper density, indicating segregation of part of the copper into grain boundaries of the polycrystalline film. Similar behaviour has been observed for other polycrystalline thin films. The effect of copper density and mobility are affected by grain boundary states.
6 citations
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TL;DR: In this paper, a two-layer model to explain the thickness dependence of conductivity and thermoelectric power of semiconducting thin films has been developed assuming that the film is a parallel combination of resistances of the three layers: the first is the interior ‘grain boundary' layer, and the other two, outer layers on opposite sides, whose conductivities are altered by the band bending.
Abstract: A two‐layer model to explain the thickness dependence of conductivity and thermoelectric power of semiconducting thin films has been developed assuming that the film is a parallel combination of resistances of the three layers: The first is the interior ‘‘grain‐boundary’’ layer, and the other two, outer layers on opposite sides, whose conductivities are altered by the band bending (and is also affected by surface‐gas interactions). The equations obtained in this model lead to an inverse thickness dependence of both the conductivity and thermoelectric power of thin films. The model is applied to analyze the conductivity and thermoelectric variation with thickness of PbTe thin films and the parameters Ug, the energy dependence of the ‘‘grain‐boundary’’ mean free path lg, and σg the surface conductivity, have been evaluated.
5 citations
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TL;DR: In this paper, the reciprocal thickness dependence of electrical resistivity observed has been explained by the effective mean free path model of classical size effect, and a reduction in conduction activation energy with increase in film thickness is accounted for by the fact that the grain size increases with thickness, and hence the barrier height decreases.
5 citations
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TL;DR: In this paper, a computer-based technique is used within the framework of the Mayadas-Shatzkes (MS) model to calculate the parameters p, R, l, and β 0.
Abstract: The temperature dependence of sheet resistance, the size effect of the temperature coefficient of resistance (TCR), and the Neel temperature for films in the thickness range 25 to 180 nm are reported. A computer based technique is used within the framework of the Mayadas-Shatzkes (MS) model to calculate the parameters p, R, l, and β0. The experimental data are in good agreement with the MS model over the entire thickness range. The Neel temperature and TCR are dependent on the substrate temperature, composition, and film thickness.
2 citations
References
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TL;DR: In this paper, the total resistivity of a thin metal film is calculated from a model in which three types of electron scattering mechanisms are simultaneously operative: an isotropic background scattering (due to the combined effects of phonons and point defects), scattering due to a distribution of planar potentials (grain boundaries), and scattering by the external surfaces.
Abstract: In this paper, the total resistivity of a thin metal film is calculated from a model in which three types of electron scattering mechanisms are simultaneously operative: an isotropic background scattering (due to the combined effects of phonons and point defects), scattering due to a distribution of planar potentials (grain boundaries), and scattering due to the external surfaces. The intrinsic or bulk resistivity is obtained by solving a Boltzmann equation in which both grain-boundary and background scattering are accounted for. The total resistivity is obtained by imposing boundary conditions due to the external surfaces (as in the Fuchs theory) on this Boltzmann equation. Interpretation of published data on grain-boundary scattering in bulk materials in terms of the calculated intrinsic resistivity, and of thin-film data in terms of the calculated total resistivity suggests that (i) the grain-boundary reflection coefficient in Al is \ensuremath{\approx} 0.15, while it is somewhat higher in Cu; (ii) the observed thickness dependence of the resistivity in thin films is due to grain-boundary scattering as well as to the Fuchs size effect; and (iii) the common observation that single-crystal films possess lower resistivities than polycrystalline films may be accounted for by grain-boundary effects rather than by differences in the nature of surface scattering.
1,842 citations
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01 Jan 1938TL;DR: In this paper, the conductivity of thin films of the alkali metals has been measured in the H. W. Wills Physical Laboratory, Bristol and the experimental results were compared with a formula derived on the basis of this hypothesis.
Abstract: The conductivity of thin films of the alkali metals has recently been measured in the H. W. Wills Physical Laboratory, Bristol*. It was found that as the thickness of the film is decreased to that of a few atomic layers the conductivity drops below that of the bulk metal. In the papers quoted the hypothesis was put forward that this effect is due to the shortening of the mean free paths of the conduction electrons of the metal by collisions with the boundaries of the film. The experimental results were compared with a formula derived on the basis of this hypothesis. This formula was, however, obtained subject to a number of simplifying assumptions, and it is the first purpose of this paper to obtain a more accurate formula. I also compare this formula with experiment, and make certain deductions about the surfaces of thin films.
1,812 citations
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TL;DR: In this article, single-crystal films of PbS, pbTe, PbSe, and SnTe have been grown on heated alkali-halide substrates.
Abstract: Single-crystal films of PbS, PbTe, PbSe, and SnTe have been grown on heated alkali-halide substrates. The temperature dependence of the mobility, Hall coefficient, and resistivity between 77\ifmmode^\circ\else\textdegree\fi{}K and 300\ifmmode^\circ\else\textdegree\fi{}K and the dependence of the magnetoresistance upon sample orientation and magnetic field strength at 77\ifmmode^\circ\else\textdegree\fi{}K have been studied. Analysis of the refractive indices, measured interferometrically in the 2.0- to 15.0-\ensuremath{\mu} region, has yielded optical dielectric constants and the direct energy gaps as functions of temperature. These studies indicate that the single-crystal films have electrical and optical properties comparable to those found in bulk material. Discussions of film formation and strain phenomena are presented and compared with the experimental results. Some of the limitations of these materials are discussed with particular emphasis on the role of structure of the films on the electrical properties.
457 citations
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TL;DR: In this article, a model for estimating effects due to electron scattering from grain boundaries, occurring simultaneously with background scattering, was developed for polycrystalline metal films in which a very fine-grained structure is often found.
Abstract: A model is developed for estimating effects due to electron scattering from grain boundaries, occurring simultaneously with background scattering. Since grain‐boundary effects are negligible in bulk materials, the model is particularly relevant to polycrystalline metal films in which a very fine‐grained structure is often found. It is shown by solution of the appropriate Boltzmann equation, that the total resistivity can be strongly dominated by grain‐boundary scattering. If grain size increases with film thickness, a marked dependence of resistivity on thickness exists, even when scattering from external surfaces is negligible or is completely specular.
393 citations
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TL;DR: In this article, an elementary theory of the optical properties of solids is described, with emphasis on the detailed development of simple models, and the results are expressed in numerical form and the use of meter-kilogram-second units throughout.
Abstract: Publisher Summary This chapter describes elementary theory of the optical properties of solids. One of the most powerful tools for studying the properties of solids is the measurement and analysis of their optical properties. Some of the results required for such an analysis are described in the chapter with emphasis on the detailed development of simple models. It expresses many of the results in numerical form and has dictated the use of meter–kilogram–second (mks) units throughout. The treatment is elementary in the sense that no physics beyond Maxwell's equations and simple quantum mechanics is used in the chapter. Dispersion relations as applied to the analysis of optical properties are discussed in the chapter. It summarizes some of the classical results for two very important physical systems, the free-electron gas and the optical lattice vibrations in ionic crystals. These systems are sufficiently simple that detailed results can be obtained very easily, yet realistic enough that the results give quite a good representation of at least some of the properties of real solids.
292 citations