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Journal ArticleDOI

Electrical conductivity of air-exposed and unexposed lead telluride thin films-temperature and size effects

14 Jan 1989-Journal of Physics D (IOP Publishing)-Vol. 22, Iss: 1, pp 162-168

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.
Topics: Grain boundary (55%), Conductivity (54%), Electrical resistivity and conductivity (53%), Thin film (53%), Lead telluride (53%)
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Journal ArticleDOI
Abstract: Copper doped zinc telluride (ZnTe:Cu) thin films have been synthesized by an electrodeposition technique from acidic aqueous bath containing ZnSO 4 , TeO 2 and CuSO 4 . The reaction mechanism has been studied by cyclic voltammetry to identify the deposition potential of ZnTe and ZnTe:Cu. X-ray diffraction as well as SEM techniques have been employed to investigate the structure and surface morphology of as-deposited and doped films. Optical properties, such as transmission, refractive index and band gap have been analyzed. The drastic change in resistivity has been observed due to incorporation of Cu dopent and the results are discussed in detail.

48 citations

Journal ArticleDOI
Abstract: Thin films of CoPc of various thickness have been deposited onto glass substrates using thermal evaporation technique at room temperature. The dark electrical resistivity measurements were carried out at different temperature range (298–423 K). An estimation of mean free path () of charge carriers in CoPc thin films and bulk resistivity, was attempted. Measurements of thermoelectric power confirm that CoPc thin films behave as p -type semiconductors. The ac conductivity ( σ ac ) has been investigated in the frequency range (10 2 –10 6 Hz) and temperature range (298–407 K). σ ac is found to be proportional to ω s where s ≈ 0.879 which is frequency and temperature independence. The ac conductivity interpreted by the correlated barrier hopping (CBH) model with centers of intimate valence alternation pairs type with a maximum barrier height, W M ≈ 1.594 eV.

35 citations

Journal ArticleDOI
M. Abdel Rafea, A.A.M. Farag1, N. RoushdyInstitutions (1)
Abstract: In this work, Cu 2 S nanocrystalline films have been successfully prepared using dip-coating technique. The stoichiometry and the structural characteristics of the prepared films were characterized by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), respectively. The surface morphology of the deposited Cu 2 S film was studied using both the scanning electron microscopy (SEM) and the atomic force microscopy (AFM). The SEM and AFM images indicate that the prepared Cu 2 S films are characterized by a well-dispersed and highly dense with spherical like-shaped aggregates of size in the nano scale. The optical absorption measurements indicate that the Cu 2 S nanoparticles have a direct band gap of 2.92 eV. The dispersion and absorption parameters such as the dispersion energy, oscillating energy, real and imaginary dielectric constants and dissipation factor were calculated within a wide wavelength range of the spectrum that indicates the suitability of the deposited films as solar absorber using this technique. The dark electrical resistivity ( ρ ) measurements were carried out at different temperatures in the range 312–440 K. These results confirm the semiconducting characteristic of the prepared Cu 2 S films. Moreover, two activation energies were obtained that indicate the presence of two dominating conduction mechanisms in these temperature ranges. The bulk electrical resistivity ( ρ B ) and the mean free path ( l 0 ) of charge carriers were estimated from the resistivity-thickness dependence. The heterojunction device of n-ZnCdS/p-Cu 2 S behaves good rectifying property. The photovoltaic characteristic of the heterojunction device using the current–voltage characteristic under illumination of 100 mW/cm 2 was also observed. Discussion of the obtained results and their comparison with the previous published data were also considered.

24 citations

Journal ArticleDOI
Manju Bala, Srashti Gupta, T. S. Tripathi1, Shikha Varma  +3 moreInstitutions (2)
11 Mar 2015-RSC Advances
Abstract: The present study focuses on the enhancement of thermoelectric power of PbTe:Ag nanocomposite thin films, synthesized by the thermal evaporation technique. Thermoelectric measurements were carried out from room temperature to 400 K. It is observed that Ag addition improves the thermoelectric power and crystalline nature of the PbTe thin films. Synchrotron based X-ray diffraction was performed to confirm the phases of the Pb–Ag–Te alloy. This was further reconfirmed by X-ray photoelectron spectroscopy (XPS) and showed the precipitation of Pb on the surface of the PbTe:Ag films. The enhancement of thermoelectric power is thus attributed to the formation of Ag2−xTe alloy and the precipitation of Pb nanostructures on the surface. The origin of such enhancement is understood based on the phenomenon of energy dependent filtering of charge carriers.

20 citations

Journal ArticleDOI
Abstract: Thin films of H2Pc of various thicknesses have been deposited onto glass substrates using thermal evaporation technique at room temperature. The dark electrical resistivity calculations were carried out at different temperatures in the range 298-473 K. Measurements of thermoelectric power confirm that H2Pc thin films behave as a p-type semiconductor. The current density-voltage characteristics of H2Pc at room temperature showed ohmic conduction mechanism at low voltages. At higher voltages the space-chargelimited conduction (SCLC) accompanied by an exponential trap distribution was dominated. The temperature dependence of current density allows determination of some essential parameters such as the hole mobility (µh), the total trap concentration (Nt), the characteristic temperature (Tt) and the trap density P (E).

17 citations

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Journal ArticleDOI
A. F. Mayadas1, M. Shatzkes1Institutions (1)
15 Feb 1970-Physical Review B
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.

1,720 citations

Journal ArticleDOI
Klaus Fuchs1Institutions (1)
01 Jan 1938-
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.

1,712 citations

Journal ArticleDOI
04 Oct 1965-Physical Review
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.

414 citations

Journal ArticleDOI
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.

344 citations

Book ChapterDOI
Frank Stern1Institutions (1)
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.

285 citations

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