Dimensional crossover of electron weak localization in ZnO/TiO stacked layers grown by atomic layer deposition

We report on the dimensional crossover of electron weak localization in ZnO/TiO stacked layers having well-defined and spatially-localized Ti dopant profiles along film thickness. These films were grown by in situ incorporation of sub-monolayer TiO on the growing ZnO film surface and subsequent overgrowth of thin conducting ZnO spacer layer using atomic layer deposition. Film thickness was varied in the range of ∼6-65 nm by vertically stacking different numbers (n = 1-7) of ZnO/TiO layers of nearly identical dopant-profiles. The evolution of zero-field sheet resistance (R) versus temperature with decreasing film thickness showed a metal to insulator transition. On the metallic side of the metal-insulator transition, R(T) and magnetoresistance data were found to be well corroborated with the theoretical framework of electron weak localization in the diffusive transport regime. The temperature dependence of both R and inelastic scattering length provided strong evidence for a smooth crossover from 2D to 3D weak localization behaviour. Results of this study provide deeper insight into the electron transport in low-dimensional n-type ZnO/TiO stacked layers which have potential applications in the field of transparent oxide electronics.