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, 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.
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.
52 citations
TL;DR: In this article, the mean free path of charge carriers in CoPc thin films and bulk resistivity was estimated using the CBH model with centers of intimate valence alternation pairs type with a maximum barrier height of 1.594 eV.
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.
38 citations
TL;DR: In this paper, the surface morphology of the deposited Cu 2 S nanocrystalline films was studied using both the scanning electron microscopy (SEM) and the atomic force microscopy(AFM).
28 citations
TL;DR: In this paper, an enhancement in the thermoelectric power (TEP) of thermally evaporated PbTe thin films by low energy Ag ion implantation was reported.
Abstract: Enhancement of the figure of merit (ZT) of thermoelectric materials is the topic of current research in energy studies We report an enhancement in the thermoelectric power (TEP) of thermally evaporated PbTe thin films by low energy Ag ion implantation This implantation results in PbTe:Ag nanocomposites Implantations were carried out at a 130 keV Ag ion beam with ion fluences of 3 × 1015, 15 × 1016, 3 × 1016, and 45 × 1016 ions/cm2 The atomic concentrations were determined using Rutherford backscattering and found to be 1 at %, 5 at %, 10 at %, and 14 at % in the implanted PbTe films Scanning electron microscopy images show the presence of fine cracks on the surface of as-deposited PbTe thin films that get shortened and suppressed and finally disappear at higher fluences of Ag ion implantation The TEP measurements, from 300 K to 400 K, show ∼25% enhancement in the Seebeck coefficient of the Ag ion implanted films in comparison to the pristine PbTe thin film The synchrotron based high resolution X-ray diffraction and X-ray photoelectron spectroscopy investigations reveal the formation of Ag2Te in the surface layer after Ag ion implantation
24 citations
TL;DR: In this article, the enhancement of thermoelectric power of PbTe:Ag nanocomposite thin films, synthesized by the thermal evaporation technique, was investigated.
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.
23 citations
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TL;DR: By starting from the Mayadas-Shatzkes model an effective mean free path l g is defined to describe electronic conduction in thin polycrystalline metallic films; the Fuchs-Sondheimer model can then be used to calculate the film resistivity and its temperature coefficient.
63 citations
TL;DR: In this article, an exact expression for the dependence of the temperature coefficient of resistivity (t.c.r.) on film thickness is derived, in order to allow a quick comparison of experimental data with the model.
60 citations
56 citations
TL;DR: In this article, the authors used the Hall-constant and conductivity as a function of temperature to determine the width of the forbidden energy gap of a semi-conductor.
41 citations
TL;DR: In this paper, the authors investigated the kinetics of oxygen adsorption on lead telluride surfaces, produced by crushing in vacuo, in the temperature range 195°K-303°K.
31 citations