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In this work, the impact of a tungsten oxide (WO3) seed and capping layer for ferroelectric La-doped (Hf, Zr)O2(La:HZO) based capacitors, designed with back-end-of-line (BEOL) compatibility, is systematically investigated. The WO3capping layer supplies oxygen to the La:HZO layer throughout the fabrication process and during device cycling. This facilitates the annihilation of oxygen vacancies (Vo) within the La:HZO layer, thereby stabilizing its ferroelectric orthorhombic phase and resulting in an increase of the remanent polarization (Pr) value in the capacitor. Moreover, the effectiveness of the WO3capping layer depends on the seed layer of the HZO film, suggesting that proper combination of the seed and capping layers should be employed to maximize the ferroelectric response. Finally, a TiN/TiO2seed layer/La:HZO/WO3capping layer/TiN capacitor is successfully fabricated and optimized by a complete set of atomic layer deposition (ALD) processes, achieving a superior 2Prvalue and endurance value of more than 109cycles at an electric field of 2.5 MV/cm. The WO3capping layer is anticipated to offer a viable solution for doped HZO capacitors with reduced thickness, addressing the challenge of elevated Volevels that favor the tetragonal phase and result in low 2Prvalues.

Recently, a step-flow growth mode has been proposed to break the inherent molybdenum disulfide (MoS2) crystal domain bimodality and yield a single-crystalline MoS2monolayer on commonly employed sapphire substrates. This work reveals an alternative growth mechanism during the metal–organic chemical vapor deposition (MOCVD) of a single-crystalline MoS2monolayer through anisotropic 2D crystal growth. During early growth stages, the epitaxial symmetry and commensurability of sapphire terraces rather than the sapphire step inclination ultimately govern the MoS2crystal orientation. Strikingly, as the MoS2crystals continue to grow laterally, the sapphire steps transform the MoS2crystal geometry into diamond-shaped domains presumably by anisotropic diffusion of ad-species and facet development. Even though these MoS2domains nucleate on sapphire with predominantly bimodal 0 and 60° azimuthal rotation, the individual domains reach lateral dimensions of up to 200 nm before merging seamlessly into a single-crystalline MoS2monolayer upon coalescence. Plan-view transmission electron microscopy reveals the single-crystalline nature across 50 μm by 50 μm inspection areas. As a result, the median carrier mobility of MoS2monolayers peaks at 25 cm2V–1s–1with the highest value reaching 28 cm2V–1s–1. This work details synthesis–structure correlations and the possibilities to tune the structure and material properties through substrate topography toward various applications in nanoelectronics, catalysis, and nanotechnology. Moreover, shape modulation through anisotropic growth phenomena on stepped surfaces can provide opportunities for nanopatterning for a wide range of materials.

Several applications of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) in nanoelectronic devices require the deposition of ultrathin pinhole free high-κ dielectric films on 2D TMDs. However, deposition of nm-thin high-κ dielectric films on 2D TMDs remains challenging due to the inert TMD surface. Here, we demonstrate that the surface of a synthetic polycrystalline 2D MoS2film is functionalized with SiO2to enable the atomic layer deposition (ALD) of thin and continuous Al2O3and HfO2layers. The origins of nucleation, the growth mode, and layer coalescence process have been investigated by complementary physical characterization techniques, which can determine the chemical bonds, absolute amount, and surface coverage of the deposited material. SiO2is prepared by oxidizing physical vapor deposited Si in air. The surface hydrophilicity of MoS2significantly increases after SiO2functionalization owing to the presence of surface hydroxyl groups. SiO2layers with a Si content of only 1.5 × 1015atoms/cm2enable the deposition of continuous 2 nm thin Al2O3and HfO2layers on MoS2at 300 °C. This fast layer closure can be achieved despite the sub-nm thickness and discontinuity of the SiO2nucleation layer. On the basis of the experimental results, we propose a nucleation mechanism that explains this fast layer closure. Nucleation of Al2O3and HfO2occurs on the SiO2islands, and fast layer closure is achieved by the lateral growth starting from the many nm-spaced SiO2islands. Finally, the dielectric properties of Al2O3on the functionalized MoS2are confirmed in a top-gated capacitor that shows a leakage current of 3.8 × 10–6A/cm2at a 3.4 nm equivalent oxide thickness. To conclude, fast nucleation and layer closure in ALD can be achieved even for a sub-nm thin, discontinuous nucleation layer. We propose that this insight can also be applied to other ALD processes, materials, or applications where thin and fully continuous layers are required.