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.