In situ one-step synthesis of p-type copper oxide for low-temperature, solution-processed thin-film transistors

Solution-processed n-type oxide semiconductors have received great interest in thin-film transistor (TFT) applications. However, solution-processed p-type oxide semiconductors are not as successful as their n-type counterparts because of the lack of material choice and their complicated fabrication procedures. In this study, a simple one-step synthetic method was employed to fabricate a p-type Cu2O thin film via in-situ reaction of a CuI film in aqueous NaOH solution at room temperature. The structure, morphology, and component variations as a function of annealing conditions (≤350 °C) were investigated. The analysis indicates that the phase evolution of Cu2O → Cu2O + CuO → CuO occurred at higher temperatures and the pure CuO phase was achieved at 250 °C. The crystallinity, average grain size, and surface morphology of the CuxO thin films were found to increase in slope as the annealing temperature increased. To explore the possible applications of the obtained CuxO films as semiconducting channel components, bottom-gated TFTs on SiO2 gate dielectrics were constructed and examined. The hole mobility of the optimized device was calculated to be 0.32 cm2 V−1 s−1, along with an on/off current ratio of 5 × 104, and a subthreshold swing of 1.1 V dec−1. The further integration of the CuxO film on an Al2O3 high-k dielectric achieves an improved device performance at 2.5 V. This work successfully demonstrates a simple method to fabricate p-type Cu-based thin films and TFTs via a solution route, which represents a great step towards the development of low-cost and all-oxide complementary metal oxide semiconductor electronics.