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 (HO) 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) plasma and ozone (O) as co-reactants for the ALD of aluminum oxide (AlO) and hafnium dioxide (HfO) on monolayer molybdenum disulfide (1L MoS) 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 O plasma oxidant damages the underlying 1L MoS via oxidation to molybdenum trioxide (MoO). No significant deleterious oxidation to MoO is observed following O-based deposition on 1L MoS, and we demonstrate the growth of HfO via thermal ALD with O co-reactant. This work reveals the impact of ALD processes on 1L MoS during the growth of high-κ dielectrics, highlighting O-based thermal ALD as a potential route for the integration of dielectric layers on 1L MoS for nanoscale optoelectronic device fabrication.