Enhanced rectification behavior and electrical properties of ZnO:Cu/ZnO heterojunctions via laser-induced doping and annealing treatments

Cu-doped ZnO:Cu/ZnO heterojunctions were fabricated via a three-step laser-induced doping technique. This study systematically investigated the electrical properties, microstructure, elemental valence states, and energy-band alignment of these heterojunctions through multiple analytical techniques. Current–voltage measurements revealed an asymmetric, nonlinear behavior due to the depletion region at the ZnO:Cu/ZnO interface, with annealing further enhancing electrical performance by yielding a lower turn-on voltage of 0.3 V, an increased rectification ratio of 81.1, and a reduced ideality factor of 6.69. Band structure analysis showed that both the conduction band offset and valence band offset at the ZnO:Cu/ZnO interface increase, indicating a higher barrier height, resulting in more pronounced rectification behavior. X-ray diffraction showed that the laser-treated samples have polycrystalline structures, and annealing improved the crystallinity, thereby enhancing the conductivity. Furthermore, secondary ion mass spectroscopy confirmed the deep implantation of high concentrations of Cu ions into ZnO. Depth-profiling x-ray photoelectron spectra revealed the co-presence of Cu+ and Cu2+, both of which contribute to the p-type conductivity. These findings offer valuable insights for optimizing ZnO heterojunctions in applications such as light-emitting diodes and laser diodes with a high level of efficiency and low turn-on voltage.