Low-Temperature Physical Adsorption for the Nucleation of Sub-10 nm Al₂O₃ Gate Stack on Top-Gated WS₂ Transistors

Two-dimensional tungsten disulfide (WS2) is one of the potential channel materials in future nanoelectronics. In this paper, an atomic layer deposition (ALD) process based on low-temperature (low-T) physical adsorption and a short purge time was used for nucleation engineering to achieve a continuous Al2O3 gate oxide with a thickness of less 10 nm on WS2. No oxidation states were observed from WS2 as revealed by X-ray photoelectron spectroscopy (XPS), indicating that the nucleation of Al2O3 gate dielectrics proceeds via the physical adsorption of reactants or precursors. The sub-10 nm thickness and the low leakage current of the Al2O3 gate oxide were validated by transmission electron microscopy (TEM) and conductive atomic force microscopy (AFM) characterizations. This high-quality Al2O3 gate oxide leads to the formation of the top-gated WS2 transistor with a low subthreshold slope.