Conductivity features of ZnO and NiO nanofiber composites

In this work, composites of ZnO and NiO nanofibers with $n$- and $p$-type conductivity, respectively, were studied. It is shown that the conductivity of the studied composites strongly depends on the arrangement of ZnO and NiO nanofibers. In the case of a mixture of ZnO and NiO nanofibers (with their random arrangement relative to each other and electrical contacts), conduction can occur only along ZnO fibers, which have a higher conductivity compared to NiO. However, the presence of the ZnO/NiO $p$–$n$ heterojunction leads to the formation of depleted regions in ZnO, as a result, the conductivity of the mixture becomes several orders of magnitude lower than the conductivity of ZnO nanofibers. In the case of a two-layer composite, in which one layer consists of NiO nanofibers and the other layer consists of ZnO nanofibers, charge carriers move through the $p$–$n$ NiO/ZnO heterojunction, which leads to a rectifying current-voltage characteristic and opens up broad prospects for the use of such systems in electronic devices.