Electrical Transport Behavior in Compositionally Modulated Lead-Telluride - Bismuth Films

A new compositionally modulated structure composed of semiconducting PbTe and semimetallic Bi was prepared with modulation wavelengths between 38-140 A. The films, deposited on mica substrates at 100(DEGREES)C, exhibited a well-defined {111} epitaxy. For shortwavelengths or a large ratio of PbTe to Bi, the Bi layers of the film apporached a quasisimple cubic structure. The dc resistivity, Hall coefficient, and magnetoresistance were measured as a function of the number (m,n) of PbTe and Bi atomic planes per modulation wavelength, the temperature (T), and the magnetic field (H). It was found that the transport properties were strongly dependent on m and n. For a series of samples with m = 12, as n increased the resistivity decreased rapidly up to n (DBLTURN) 8 and it oscillated with a period of n (DBLTURN) 8 (32A) for n (GREATERTHEQ) 8. The oscillatory behavior was also observed in the Hall coefficient and magnetoresistance, and its period strongly correlated with that of the resistivity. These results are believed to be the maifestation of the quantum size effect, associated with carrier confinement in the Bi layers of the modulated films. The sheet resistance R(,(SQUARE)) of all commensurate samples displayed a logarithmic dependence at low temperatures ((LESSTHEQ) 10 K) with a prefactor that oscillated with n. At low temperatures, R(,(SQUARE)) also showed a logarithmic dependence on the magnetic field (5 kG (LESSTHEQ) H (LESSTHEQ) 50 kG) in both perpendicular and parallel directions of the field for the samples having m (GREATERTHEQ) 12. These features are in good agreement with the recent theories on localization and Coulomb interaction in weakly localized two-dimensional systems. It was found that the magnetic field dependence was mainly due to the localization effect, including spin-orbit scattering and Zeeman spin splitting, while the temperature dependence was dominated by the interaction effects. The characteristic two-dimensional parameters were extracted from detailed computer fits of the data. The logarithmic behavior disappeared with annealing and this argues against the possibility of a Kondo effect in the observed behavior. For incommensurate samples having R (GREATERTHEQ) 8 K(OMEGA)/(SQUARE), the resistance was better fitted by a exp(1/T) dependence indicating that the samples displayed a strongly localized behavior.