Solution-processed cobalt doping for performance enhancement of p-type NiO thin-film transistors

Oxide semiconductors have become key materials in electronic applications. However, the electrical performance of p-type oxides remains inferior to that of n-type oxides, which is a critical limitation that hinders the application of complementary metal–oxide–semiconductor (CMOS) based on oxide semiconductors. Therefore, enhancing the electrical performance of p-type oxide thin-film transistors (TFTs) is crucial to achieve the performance standards required for CMOS applications. Herein, we report solution-processed p-type NiO TFTs with an enhanced field-effect hole mobility (0.32 cm² V⁻¹ s⁻¹) and on–off current ratio (3.3 × 10³), which have been achieved by optimizing the thermal annealing and cobalt doping parameters. An annealing temperature of 500 °C and a cobalt doping concentration of 10 at.% provide the highest hole mobility and on–off current ratio. The enhancement mechanism in the p-type NiO channel is analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy. The spectroscopic analysis reveals the effect of the characteristics of the NiO thin films, such as the energy bandgap, crystallinity, and Ni–O bonding characteristics, on the electrical properties of the p-type NiO TFTs. Our findings provide insights for further improving the electrical performance of p-type oxide semiconductors.