Impact of Co-Reactants in Atomic Layer Deposition of High-κ Dielectrics on Monolayer Molybdenum Disulfide

The integration of single-layer transition metal dichalcogenides (TMDCs) in nanoscale field-effect transistor devices requires the deposition of a high dielectric constant (high-kappa) material to act as the gate dielectric. Traditional thermal atomic layer deposition (ALD) is commonly used to deposit dielectrics on three-dimensional substrates, but ALD of high-kappa materials on monolayer TMDCs is more challenging. Thermal ALD with water (H2O) co-reactant often results in incomplete and nonuniform dielectric growth on atomically thin TMDCs, owing to a chemically inert basal plane. The development of alternative ALD processes for the realization of dielectric layers on monolayer TMDCs is therefore important. Here, we study oxygen (O-2) plasma and ozone (O-3) as co-reactants for the ALD of aluminum oxide (Al2O3) and hafnium dioxide (HfO2) on monolayer molybdenum disulfide (1L MoS2) films. By employing a robust characterization process that combines atomic force microscopy, Raman/photoluminescence spectroscopy, and X-ray photoelectron spectroscopy, we reveal growth of high-kappa dielectrics by plasma-enhanced ALD with O-2 plasma oxidant damages the underlying 1L MoS2 via oxidation to molybdenum trioxide (MoO3). No significant deleterious oxidation to MoO3 is observed following O-3-based deposition on 1L MoS2, and we demonstrate the growth of HfO2 via thermal ALD with O-3 co-reactant. This work reveals the impact of ALD processes on 1L MoS2 during the growth of high-kappa dielectrics, highlighting O-3-based thermal ALD as a potential route for the integration of dielectric layers on 1L MoS2 for nanoscale optoelectronic device fabrication.