Power-law currents in some ZnO-Sn composite materials

Abstract

The dependence of current density on applied voltage has been studied in the composite system ZnO-Sn, where the proportion of Sn was 5% or 10% by weight. All samples showed a power-law dependence of current density on voltage, with the exponent being either equal to 2 or in the range 2.6-2.9. The conductivity was ascribed to traps of density 1*1016-2*1017 cm-3 which are situated below the conduction band edge of the ZnO. In some cases the traps were distributed exponentially according to the relation N(E)=N0exp(-E/kTt), where the temperature parameter Tt was typically about 500-600K; in other cases the traps were situated at a single level of 0.255-0.366 eV below the conduction band.