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-κ) 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-κ 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 (O₂) plasma and ozone (O₃) 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-κ dielectrics by plasma-enhanced ALD with O₂ plasma oxidant damages the underlying 1L MoS₂ via oxidation to molybdenum trioxide (MoO₃). No significant deleterious oxidation to MoO₃ is observed following O₃-based deposition on 1L MoS₂, and we demonstrate the growth of HfO₂ via thermal ALD with O₃ co-reactant. This work reveals the impact of ALD processes on 1L MoS₂ during the growth of high-κ dielectrics, highlighting O₃-based thermal ALD as a potential route for the integration of dielectric layers on 1L MoS₂ for nanoscale optoelectronic device fabrication.