Engineering of Exciton Dynamics and Interactions in Atomically thin Semiconducting Materials

Abstract

The thesis explores the significance of novel two-dimensional (2D) ultra-thin materials within the materials science and nanotechnology communities. Driven by their captivating electrical and optical characteristics, these materials, often exfoliated from layered structures, exhibit weak interlayer van der Waals (vdW) forces, enabling facile thinning to atomic thickness. While graphene, with its zero bandgaps, laid the foundation for 2D materials research, this thesis focuses on Transition Metal Dichalcogenides (TMDs), a prominent 2D semiconducting family with bandgaps suitable for optoelectronic applications. The reduced physical dimensions of TMD monolayers, especially the quantum confinement effect, play a crucial role in modulating TMD properties, intensifying many-body interactions compared to bulk semiconductors.

The experimental emphasis lies in demonstrating the properties of quasi-particles such as excitons, trions, and biexcitons, with a focus on engineering exciton dynamics, many-body effects among quasi-particles, enhanced light-matter interactions and higher tunability for future optoelectronic and quantum device applications. The thesis firstly delves into TMD/metal junctions, exploring interlayer charge transfer effects and dielectric screening effects. The first half explores the optical properties and exciton properties of traditional 2D single-layer TMD materials. The second half focuses on interlayer excitons in TMD hetero-bilayers, showcasing complex many-body interactions, effective engineering control, and revealing a higher level of tunability through the customizable interface. The thesis reports the first demonstration of free interlayer biexciton in TMD heterostructures, and also a built-in electric field-induced Stark effect in a 1L graphene/1L TMD heterostructure. A substantial Stark shift and polarizability are achieved in fabricated heterostructure and efficient heterostructure-based photodetectors are demonstrated, expanding tunability for excitons and applications in photodetectors and quantum light sources. The thesis concludes by exploring application devices of 2D artificial microstructures, integrating intrinsic materials and nanofabricated structures for enhanced light-matter interactions.

In summary, the thesis offers a comprehensive exploration of excitonic interactions in 2D semiconducting materials and their vdW stacked heterostructures. It demonstrates optical tunability, control over dipolar systems, and promising characteristics for next-gen optoelectronics and quantum applications. The results contribute deep insights into many-body effects and light-matter interactions in quantum-confined 2D systems, setting them apart in semiconductor and material science. Show more