The anisotropy of the electrical conductivity and the electrical piezoeffect due to this anisotropy is found in a uniaxially deformed thin polycrystalline Bi film. The symmetrical and antisymmetrical parts of the nondiagonal elements of the conductivity tensor for various directions of the deformation in the presence of an external magnetic field are investigated. It is shown that all features of the anisotropy can be qualitatively explained in terms of electron repopulation between the L‐valleys in the randomly orientated and deformed Bi microcrystallites. Possible ways of obtaining higher anisotropy in deformed films are discussed.
The magnetoresistance (MR), sheet resistance (R ), and structure of vacuum-deposited thin bismuth films with 0.3 to 1.5 µm thickness prepared on noncrystalline dielectric amorphous substrate were investigated as a function of substrate (TS) and annealing (TA) temperatures. The investigations were mainly focused on films prepared at critical TS and TA temperatures, at which essential changes in film structure and magnetoresistance value were obtained. The existence of these temperatures is associated with the intensive growth of high-quality crystallites. The mechanism of this phenomenon is discussed. In the case of annealed 1-1.5 µm thick films, the size of these crystallites ranges from 50 to 200 µm. It was demonstrated that such films have large transverse magnetoresistance ranging up to 170% for 1.5 µm thick films at 293 K in 2.5 T magnetic fields.
This paper reports an investigation of the large magnetoresistance (MR) of 0.3 -1.5 µm thick polycrystalline Bi films deposited in vacuum on non-crystalline substrates and annealed at critical temperatures. The occurrence of critical temperatures is associated with intensive growth of crystallites. It is demonstrated that such films consist of large 50 -200 µm high-quality crystallites and exhibit a large transverse MR. At temperatures higher than 77 K the magnitude of the MR can exceed that of epitaxial Bi films. The experimental results are interpreted on the basis of a polycrystalline Bi thin-film model. The data suggest that in Te-doped Bi films the MR can be larger than that in pure Bi films. It is found that the grainboundary scattering is weak. However, there exist rather isotropic extra carrier scattering channels which reduce the anisotropy of electrical conductivity and MR. The relative importance of this extra scattering changes with temperature.
The strong electrical piezoeffect caused by the deformation induced anisotropy of electron mobility in Bi, _,Sb, semiconducting samples is described. Attention is drawn to the piezoeffect voltage, high in undoped samples, its nonsymmetric change under tensile and compressive deformation, and its sign inversion at small magnetic fields. All these effects are explained in terms of electron intervalley repopulation and scattering. Possible applications are discussed.
We have investigated the magnetoresistance of thin polycrystalline semiconductor Bi 1−x Sb x films prepared on a flat fibreglass substrate at a temperature of 77 K using pulsed magnetic fields up to 50 T. For these investigations we used films exposed to different thermal annealing and having different grain structures. Negative magnetoresistance was obtained in semiconductor polycrystalline thin films affected by longitudinal magnetic fields to fields in excess of 20 T. This phenomenon has been qualitatively explained in terms of microcrystallites, which are energy band structure changes induced by strong magnetic fields. It is shown that, by measuring the magnetoresistance in strong and quantizing magnetic fields, we can determine the composition and quality of thin Bi-Sb films.
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