The electrical dc resistivity of variously prepared polymerconducting-carbon-black composites has been studied over a wide temperature range (4.2 -300 K). For the different composites, the resistivity follows a lnp-T law over the whole temperature range, with the a parameter, varying between -, ' &a& -', determined by the carbon-black concentration and the dispersion in the carbon grain sizes. The experimental facts can be understood on the basis of a critical-pathmethod analysis for hopping conduction developed for granular disordered metallic systems.
Metal-doped semiconductor-metal tunnel junctions for which the tunneling barrier is made of a double Schottky barrier are proposed and studied both experimentally and theoretically. Using the tunneling barrier model, the electron tunneling current is calculated. The junctions are prepared by successive condensation from vapor of a P b electrode, a CdS layer, and 5~ second P b electrode. The thickness of the semiconducting layer is varied from 50 t o 5000 A. The I-U characteristics of the junctions are measured a t liquid helium temperature and prove to be in good agreement with the theory proposed.Xous avons propose et Btudi6 tant thboriquement qu'expi.rlmentalement, des jonctions tunnel, metal-semi-conducteur (dop&)-metal, pour lesquelles la barrihre tunnel est constituee d'une double barribre Schottky (deux contacts metal-semi-conducteur accoles dos A dos). Nous avons calculh pour ce modble de barrikre le courant tunnel. De telles jonctions ont Bte rbalishes par evaporation thermique, l'bpaisseur de la couche semiconductrice (CdS) variant de 50 & 5000 A. Les caractbristiques blectriques de ces jonctions ont 6tb mesnrkes aux temperatures de l'hblium liquide. Les rbsultats exphrimentaux sont en accord avec les conclusions de la thhorie proposbe.
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