Post-Treatment of Monolayer MoS2 Field-Effect Transistors with H2O Vapor: Alleviation of Remote Channel Doping

Atomic layer deposition (ALD) of high-k dielectric films on MoS₂ channels can lead to inadvertent remote electron doping of channels owing to nonequilibrium ALD conditions, such as the low temperatures and short purge times required for pinhole-free coating, as well as the weak physical adsorption of ALD precursors on MoS₂. In this study, we propose the application of a simple and effective H₂O vapor post-treatment (H₂O PT) at 100 °C immediately after complete integration of bottom- and top-gate monolayer MoS₂ field-effect transistors (FETs), to address the inadvertent channel doping effect. When H₂O PT was applied to bottom-gate monolayer MoS₂ FETs with an ALD-Al₂O₃ passivation layer, the mitigation of channel doping was confirmed through electrical and optical measurements. Chemical analyses indicated that H₂O PT alleviated the remote doping effect by reducing the number of C/H impurities and possible oxygen defects near the ALD-Al₂O₃/MoS₂ interface. These impurities and defects were associated with the incomplete reaction of the ALD precursor due to the nonequilibrium ALD used for the complete coating of Al₂O₃ on MoS₂. Applying H₂O PT to top-gate monolayer MoS₂ FET arrays significantly narrowed the distributions of the threshold voltage and subthreshold swing. Moreover, it reduced the gate dielectric leakage current induced by the dielectric damage incurred during physical vapor deposition of the gate electrode. Finally, the time-dependent stability of top-gate monolayer MoS₂ FETs subjected to H₂O PT was confirmed for at least two months in air.