Annealing-induced modifications on structural, surface chemical bonding, and electrical characteristics of p-NiO/n-TiO 2 heterostructure

The influences of annealing temperatures on the electrical characteristics of a p-NiO/n-TiO 2 heterojunction diode were thoroughly investigated, taking into account changes in microstructure, morphology, and surface chemistry of the p-NiO/n-TiO 2 films, which were deposited on an insulating SiO 2 /Si layer. During different annealing processes, considerable stress variations were observed in the p-NiO/n-TiO 2 films due to the crystalline evolution of p-NiO and n-TiO 2 . Notably, the crystallization of the TiO 2 layer, which serves as the intermediary between the back contact materials and NiO, led to the evident formation of grain structures. As the annealing temperature increased, the surface roughness also grew from 5.4 to 8.7 nm. At an annealing temperature of 500 °C, the formation of a parasitic NiTiO x phase was observed, particularly at the interface between NiO and TiO 2 . Conversely, the study also revealed that annealing temperature played a significant role in the rectifying behavior, barrier potential, and ideality factor of the diode. Among the various annealing processes, the most favorable results were achieved after annealing at 400 °C. At this temperature, the diode demonstrated the lowest ideality factor of 1.89, accompanied by superior rectifying behavior and a barrier potential of 0.70 eV. The findings clearly indicate that any alterations in the surface chemistry and microstructure of the film directly impact the diode's characteristics. Thus, optimizing the annealing temperature becomes crucial for enhancing the performance of the p-NiO/n-TiO 2 heterojunction diode.