Journal ArticleDOI

# Anomalous variation of resistance in bismuth thin films and the effect of substrate temperature

01 Mar 1981-Vacuum (Pergamon)-Vol. 31, Iss: 3, pp 133-136

TL;DR: In this paper, the resistance of bismuth thin films of thickness 720 A have been vacuum deposited at various substrate temperatures on glass substrates and their resistances are recorded as a function of temperature after annealing the films at 200°C.

AbstractBismuth thin films of thickness 720 A have been vacuum deposited at various substrate temperatures on glass substrates and their resistances are recorded as a function of temperature after annealing the films at 200°C. The resistance (R) versus temperature (t) curves show anomalous behaviour, in that the resistance first decreases as the temperature increases and then increases as the temperature increases, thus showing a minimum in resistance, Rmin at a temperature tmin. The position of Rmin (i.e. tmin) and the magnitude of Rmin vary with substrate temperature. However, no such anomalous behaviour is observed for the film deposited at room temperature and its resistance monotonically decreases with increase in temperature. These observations have been explained by considering that the bismuth films behave as narrow band gap semiconductors because of the quantum size effect and by the facts that in polycrystalline films the electronic mean free path will be limited by the grain size and also that the average grain size of the film increases as the substrate temperature during deposition increases.

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E.I. Rogacheva
TL;DR: In this paper, the authors attribute this oscillatory behavior to quantum-size effects, which are observable when the electron mean-free path and Fermi wave length exceed the film thickness d.
Abstract: Oscillatory thickness dependences of the electrical conductivity, Hall coefficient, charge carrier mobility, and Seebeck coefficient were obtained at room temperature for n-type thin Bi films (d=3–300 nm) fabricated by the thermal evaporation of a bismuth crystal in a vacuum and deposition on mica substrates at 380 K. We attribute this oscillatory behavior to quantum-size effects, which are observable when the electron mean-free path and Fermi wave length exceed the film thickness d.

52 citations

Journal ArticleDOI
TL;DR: In this paper, the electrical resistance of Ag2Te films has been measured as a function of temperature during heating, which was carried out immediately after the film formation, and the observed exponential decrease of resistance with temperature up to the transition point points to the semiconducting nature of the low temperature polymorph of ag2Te.
Abstract: Thin films of Ag2Te of various thicknesses in the range 500–1500 A have been prepared by thermal evaporation of the compound under vacuum on clean glass substrates held at room temperature. The electrical resistance of the films has been measured as a function of temperature during heating, which was carried out immediately after the film formation. The observed exponential decrease of resistance with temperature up to the transition point points to the semiconducting nature of the low temperature polymorph of Ag2Te. The band gap of the low temperature phase is calculated for various thicknesses of the films and it is found that the band gap is a function of film thickness, increasing with decreasing thickness. The increase in the band gap, which was found to be inversely proportional to the square of the film thickness, is attributed to quantization of electron momentum component normal to film plane.

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Journal ArticleDOI
TL;DR: In this paper, electrical resistivity and Hall effect measurements have been made on vacuum evaporated Bi 90 Sb 10 alloy films of various thickness (350 A to 4500 A), in the temperature range of 77 to 510 K.
Abstract: The electrical resistivity and Hall effect measurements have been made on vacuum evaporated Bi 90 Sb 10 alloy films of various thickness (350 A to 4500 A), in the temperature range of 77 to 510 K. As observed earlier, the alloy system behaves like a semiconductor, but with a band gap quite higher than previously reported for bulk single crystals. Also a kind of intergrain barrier is found in these films. The activation energy of these barriers is found to decrease with increasing film thickness and substrate temperature. This trend agrees with the earlier observations in other materials and also in the same alloy system. The higher band gaps in these films are attributed to quantum size effect and high dislocation density in these films. The decrease in the inter-grain barrier activation energy with increasing thickness and substrate temperature has been attributed to increased grain size of the films.

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Journal ArticleDOI
TL;DR: In this paper, the initial lattice distortion energy spectra of as-grown bismuth thin films have been evaluated and it is found that the defects have preferential activation energy values around 1.06 eV, 1.14 eV and 1.32 ev.
Abstract: Bismuth thin films of various thicknesses between 15 nm and 350 nm were vacuum deposited at room temperature on to glass substrates, immediately after which they were twice heat treated at a uniform rate. During the heat treatment, the resistance changes were monitored and, using these data, the initial lattice distortion energy spectra of as-grown bismuth thin films have been evaluated. It is found that the defects have preferential activation energy values around 1.06 eV, 1.14 eV and 1.32 ev. It is also found that ∫F0 (E) dE oscillates with thickness, which is attributed to the quantum size effect.

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Journal ArticleDOI
01 Jan 1981-Vacuum
TL;DR: In this article, it was shown that resistivity oscillates with thickness both for unannealed and annealed films and that the same kind of oscillatory behaviour with thickness is also observed in the case of defect resistivity.
Abstract: Bismuth thin films of various thicknesses in the range 150–3500 A have been vacuum deposited on clean glass substrates held at room temperature. Resistances were measured both before and after heat treatment in situ, which was carried out immediately after film formation. It is found that the resistivity oscillates with thickness both for unannealed and annealed films. The same kind of oscillatory behaviour with thickness is also observed in the case of defect resistivity. It is argued that the above oscillatory behaviour is due to the oscillatory behaviour of mobility with thickness. It has also been pointed out that the mobility due to scattering by point defect clusters also oscillates with thickness, if the range of the scattering potential is taken to be of the order of the linear dimensions of the clusters.

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01 Jan 1969

2,180 citations

Journal ArticleDOI
TL;DR: The electrical resistivity and Hall effect of zone-levelled single crystals of Bi-Sb alloys have been measured in the temperature range from 4.2 to 300 K as discussed by the authors.
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198 citations

Journal ArticleDOI
TL;DR: The thickness dependence of the electrical properties of thin epitaxial bismuth films (of thickness 2-3 μm) was studied at 42 and 77 K in this article.
Abstract: The thickness dependence of the electrical properties of thin epitaxial bismuth films (of thickness 02–3 μm) was studied at 42 and 77 K The size effect theory developed by Mayadas and Shatzkes was modified so that it could be applied to a system with two carriers (electrons and holes) The thickness dependence of the carrier densities was also taken into account The specularity parameter P at the surface and the reflection coefficient R at the grain boundaries were determined to be 07 and 02–03 respectively It should be noted that the effect of scattering of the carriers at the grain boundary planes parallel to the electric field could not be neglected

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Journal ArticleDOI
TL;DR: In this paper, anomalous behavior of the thermoelectric power of thin Bi films has been observed and the results are consistent with those anticipated, based on both quantum and classical size effects in scattering.
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Journal ArticleDOI
TL;DR: In this article, the magnetic field dependence of σ xx and σ yx, calculated from an analysis of the data on ϱ, Δϱ/ϱ and the Hall e.m.f., and using the formula of the two-band model for strong and weak magnetic fields, was obtained.
Abstract: The resistivity ϱ of bismuth films in the absence of a magnetic field exhibits the following features: it decreases with increasing temperature T ; the temperature dependence of the resistance has a maximum at low temperatures for very thin films and a minimum at higher temperatures for films of larger thickness; below 1000 A the conductivity increases with decreasing film thickness L (anomalous size effect); the classical size effect appears as the film thickness increases. For very thin films the magnetoresistance coefficient (in the region ωτ T : at a certain temperature determined by the film thickness a minimum appears and then an anomalous rise in magnetoresistance. From an analysis of the magnetic field dependence of σ xx and σ yx , calculated from our data on ϱ, Δϱ/ϱ and the Hall e.m.f., and using the formula of the two-band model for strong and weak magnetic fields, we obtained the change in concentration ( n,p ) and mobility (μ, ν) of the charge carriers with varying T and L , and hence we were able to explain the observed features of their kinetic properties. The appearance of anomalies results both from the resonance scattering of carriers under size quantization and from the non-uniformity of the distribution through the film thickness of carriers of different sign due to potential bending near the surface. This leads to a shift in the electron spectrum characteristics with decreasing Bi film thickness.

13 citations