Atomic Layer Deposition
RESOURCES
Treatments to control the optical, electronic, and structural properties of monolayer MoS2 films
- Author
- Brendan Finbarr Murphy Healy
- Year
- 2025
- Abstract & Cover
- Source of Information
- http://wrap.warwick.ac.uk/194328
- University
- University of Warwick (Coventry, United Kingdom)
- External Link
Molybdenum disulfide (MoS2) has emerged as a semiconducting alternative to graphene for nanoscale optoelectronics, exhibiting novel optical and electronic properties at single-layer thickness. The scalable integration of monolayer MoS2 (1L MoS2) in mass-produced devices requires large-area monolayer films, typically grown via chemical vapour deposition (CVD). Despite favourable photoluminescence, the emission efficiency from untreated 1L MoS2 is poor, limiting its practical optoelectronic suitability. Moreover, the realisation of MoS2-based field-effect transistors demands the deposition of high dielectric constant (high-κ) materials. Growth of uniform high-κ layers on 1L MoS2 via traditional thermal atomic layer deposition (ALD) is challenging, and the dielectric growth characteristics on CVD-1L MoS2 are not well understood.
Here, the characterisation and treatment of commercially available CVD-grown 1L MoS2 films are investigated. Spatial variability in the structural and optical properties of CVD-1L MoS2 is revealed, and a robust characterisation process for assessment of treatment-induced modifications is developed. Two general treatments of 1L MoS2 are explored and are found to have opposing effects on the optical performance: immersion in the superacid bis(trifluoromethanesulfonyl)amide (TFSA) and ALD of either aluminium oxide (Al2O3) or hafnium dioxide (HfO2) films via water (H2O) co-reactant. Tuneability of the optical properties of CVD-1L MoS2 is demonstrated via selection of the applied treatment.
Alternative co-reactants for ALD of high-κ dielectrics on CVD-1L MoS2, namely oxygen (O2) plasma and ozone (O3), are explored, and the impacts on MoS2 are evaluated. Plasma-enhanced ALD (PEALD) with O2 plasma is found to oxidise MoS2 to MoO3, but successful growth of HfO2 via O3-based ALD is demonstrated. The nucleation and growth behaviours of Al2O3 and HfO2 films grown on CVD-1L MoS2 via H2O-based thermal ALD are also studied.
This thesis highlights various external treatments that can modify the optical, electronic, and structural properties of CVD-1L MoS2 films for optoelectronic applications
