Impact of hydrogen plasma treatment on the electrical performances of ZnO thin-film transistors

Abstract

In this study, we investigated the effects of hydrogen plasma (H) treatment on the structure, surface morphology, and optical and electronic properties of zinc oxide (ZnO) films, and on the performances of related ZnO thin-film transistors (TFTs). It was found that the performances and stabilities of the ZnO TFTs improved by carrying out the appropriate H plasma treatment. As a result, the ZnO:H (30 s) TFTs were found to exhibit a high field-effect mobility of 18.5 cm2/Vs, small threshold voltage (Vth) of 1.5 V, low sub-threshold swing of 0.32 V/decade, and high on/off current ratio (Ion/Ioff) of 107. These improvements could be attributed to the fact that the H treatment of ZnO was shown to result in the generation of shallow donors and in the defect passivation in ZnO films owing to the formation of HO and VO-H complex bounds. The increase in the carrier concentration and the passivation of the interface trap densities and oxygen vacancies in ZnO TFTs were revealed by X-ray photo-electron spectroscopy (XPS) analysis and density functional theory (DFT) calculations. These high-performance hydrogenated ZnO TFTs obtained as a result may find applications in oxide thin-film electronics.