Thin films of Pb0.8Sn0.2Te of varying thicknesses deposited by the flash evaporation method showed considerable change in resistance with time when exposed to oxygen or atmosphere. The change in resistance is found to decrease with increase in thickness and with increase in substrate temperature. The observed behaviour is explained by an oxygen adsorption model, which is further supported by the x-ray photoelectron spectroscopy (XPS) of the films.

C. Bahulayan

V. Damodara das

Adsorption

Characterization

Deposition

Electric resistance

Oxygen

Semiconducting Lead Compounds

Substrates

Surfaces

Thermal effects

Transmission electron microscopy

X ray crystallography

X ray photoelectron spectroscopy

FLASH EVAPORATION METHOD

LEAD TIN TELLURIUM

OXYGEN ADSORPTION MODEL

Thin films

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IIT Madras

Effect of oxygen adsorption on the electrical resistance of thin films

Semiconductor Science and Technology

Thin films of different thicknesses have been vacuum (2 × 10-5 torr) deposited by the flash evaporation technique onto glass plates held at room temperature. In situ measurement of electrical resistance in vacuum (2 × 10-5 torr) as a function of time was carried out until the resistance stabilized. Then, on exposure to air by controlled admittance of air into the vacuum chamber, it was found that the resistance of the films increased as pressure increased. After air was admitted up to atmospheric pressure, the resistance was also found to increase as a function of time in the atmosphere. Also, it was observed that the resistance of the film during re-evacuation does not retrace the previous path during the exposure of the films and thus the resistance variation is not reversible. The variation of resistance taking place in the films in vacuum with time is attributed to the coalescence process. The agglomeration rates for the films of different thicknesses were obtained from the linear behavior of In(R/R0) vs time plot. The resistance variation of the films during the exposure to air is attributed to oxygen adsorption. It was found that the annealed films are less influenced by the exposure compared to the as-grown films. Adsorption of oxygen takes place on the external and internal surfaces of the films. The films were found to be ESR active. Structural analysis was carried out using the XRD and TEM techniques. © 1998 Elsevier Science Ltd. All rights reserved.

Solid State Communications

Time dependent electrical resistance of Bi2(Te0.4Se0.6)3 thin films in vacuum and on exposure to atmosphere

Photoelectrochemical (PEC) solar cells made using as-grown polycrystalline thin films of n-CdSe0.6Te0.4 (thickness ≈ 5000 Å) (prepared by vacuum thermal flash evaporation with a deposition rate of 20 ± 1 Å s-1 in a vacuum better than 5 × 10-5 torr on indium oxide coated microslide glass plates [σ = 1.25 × 104 (Ω-cm)-1] held at 200°C) dipped in aqueous ferro-ferricyanide electrolyte have been studied to evaluate the conversion efficiency under white light illumination intensity of 100 mW cm-2 (AM1). Mott - Shottky plots have been drawn (in the dark condition) to evaluate the semiconductor parameters. The reasons for the observed high power conversion efficiency and high quantum efficiency in relation to the semiconductor parameters are explained. The films have been characterized by X-ray diffraction for structural studies, Energy Despersive Analysis of X-rays (EDAX) for compositional analysis, Scanning Electron Microscopy (SEM) technique for surface morphology studies and optical absorption for band gap determination. © 1997 Elsevier Science Ltd.

Power conversion efficiency studies of vacuum evaporated n-CdSe0.6Te0.4 semiconducting thin film/(aq) ferro-ferricyanide electrolyte photoelectrochemical solar cells

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. © 1989 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

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

Lead telluride and lead selenide films were prepared by the thermal evaporation technique on clean glass substrates held at room temperature in a vacuum of 3×10-5 Torr. The resistance of the films was measured at different air pressures. The resistance of the as-grown films was found to be of the order of a kilohm but increased with increasing pressure. A resistance maximum was observed at a particular air pressure after which the resistance decreased with increasing pressure. An indirect method, namely, the measurement of the conductivity variation as a function of air pressure, has been used to estimate the extent of air adsorption and the adsorption isotherms have been drawn on this basis. The dependence of adsorption on thickness is also discussed. © 1985 The American Physical Society.

Physical Review B

Electrical-conductivity changes in PbTe and PbSe films on exposure to the atmosphere

Bulletin of Materials Science

Electron microscopic studies of vacuum-evaporated (Pb1 −x Sn x )1 −y Te y thin films

Journal of Materials Science

Electrical transport properties of thallium-doped p-type Pb0.8Sn0.2Te thin films

Effect of oxygen adsorption on the electrical resistance of Pb0.8Sn0.2Te thin films

Journal	Semiconductor Science and Technology
ISSN	02681242
Open Access	No