ZnO/Ag/graphene transparent conductive oxide film with ultrathin Ag layer

Abstract

We insert a silver (Ag) layer between zinc oxide (ZnO) and graphene films of a bilayer structure to create trilayer transparent conductive oxide films with improved conductivities due to the bridge provided by the Ag layer to transport free electrons. To construct trilayer ZnO/Ag/graphene transparent conductive films, the Ag and ZnO layers are deposited successively on a graphene/glass substrate by magnetron sputtering from solid Ag and powder ZnO targets. The results show that the electron concentration in the trilayer films increases one order of magnitude to 1021 cm−3 upon inserting dispersed Ag dots and three orders of magnitude to 1023 cm−3 upon adding a relatively continuous 10.5-nm-thick Ag layer. However, the electron mobility drops dramatically from 10−1 to 10−2 cm2 V−1 s−1 because the dispersed Ag dots of a thin Ag layer form narrow bridges, which limit electron transport. The continuous 10.5-nm-thick Ag layer not only acts as a wide bridge but also provides electrons; therefore, the resistivity of the ZnO/Ag(continuous)/graphene trilayer decreases significantly, while the mobility of the trilayer film remains of the same order of magnitude as that of the continuous Ag layer. Of course, the transparency of the trilayer film decreases slightly upon inserting the Ag layer. To create frontier electrodes, the ZnO/Ag/graphene multilayer structure must be built up to form transparent conductive oxide films.