Exploring the integration of two-dimensional WS2 with near lattice matched III-nitride semiconductors

Mathew, Annie ORCID: https://orcid.org/0000-0003-3233-5609 2024. Exploring the integration of two-dimensional WS2 with near lattice matched III-nitride semiconductors. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDC) have attracted considerable interest owing to the possibility to create next generation nano- and opto�electronic devices. Among them, 2D tungsten disulphide (WS2) has emerged as unique candidate for future nanotechnologies due to its superior optical, electrical and thermal properties. Manipulating these materials by unconventionally stacking them or intercalating with foreign atoms in van der Waals heterostructures opens further possibilities for interesting physical phenomena and novel nanodevice applications. Underlying substrates play an important role in tuning the electronic and optical properties of these 2D materials. The formation of group III-nitride semiconductor based heterostructures is essential for optoelectronic applications, however, is greatly limited due to the impact of lattice mismatch. Integrating 2D materials on lattice matched III-nitride semiconductors can lead to surface reconstruction and can induce interface effects creating novel electronic and optical properties in the heterostructure. In this thesis, I present the effect of nearly lattice matched III-nitride semiconductor substrates on the material properties of 2D WS2. First, density functional theory calculations were used to explore the electronic band, linear and non-linear optical properties of the heterostructures. The integration of WS2 monolayer on GaN exhibits the strong thickness dependence of the band gap, band alignment and optical absorption. Then, the optical properties of exfoliated thin layer WS2 on SiO2/Si and GaN substrates were investigated revealing quantum confined Stark effect in WS2/GaN heterostructure. Finally, direct CVD growth of high-quality atomically thin WS2 on near lattice matched GaN and AlN and typically used SiO2/Si and sapphire substrates were demonstrated. The suitable growth conditions for creating near lattice matched 2D/3D van der Waals heterostructures were established. With this work, new insights into lattice matched 2D TMDC on III-nitride semiconductor heterostructures have been demonstrated. These results can pave the way towards their synthesis and fabrication in opto- and nano- electronic devices.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	2D TMDC, WS2, III-nitrides, van der Waals heterostructure, lattice matching, band alignment, CVD.
Funders:	EPSRC
Date of First Compliant Deposit:	29 July 2024
Last Modified:	29 Jul 2024 15:36
URI:	https://orca.cardiff.ac.uk/id/eprint/170988

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