Repair of Oxygen Vacancies and Improvement of HfO 2 /MoS 2 Interface by NH 3 -Plasma Treatment

The effects of treating the HfO ₂ gate dielectric in different plasmas (O ₂ , N ₂ , and NH ₃ ) on the electrical characteristics of a back-gated MoS ₂ transistor are investigated. It is found that the electrical properties of the device improved after HfO ₂ is treated by these plasmas, in which NH ₃ -plasma treatment results in the best electrical characteristics: high ON–OFF ratio of $1.26\times 10^{{7}}$ , high extrinsic carrier mobility of 61.5 cm ² / $\text{V}\cdot \text{s}$ , small subthreshold swing (SS) of 111 mV/dec, low interface-state density of $2.79\times 10^{12}$ eV $^{-{1}}\,\,\cdot $ cm ⁻² , and small hysteresis of 43 mV. These should be attributed to the incorporation of more N into the HfO ₂ film by the NH ₃ plasma to repair the oxygen vacancies and increase the $k$ value of the HfO ₂ film. Moreover, H from the NH ₃ plasma effectively passivates the dangling bonds at/near the HfO ₂ /MoS ₂ interface, thus creating an excellent MoS ₂ /HfO ₂ interface.