Advanced Epitaxy on 2D Materials for Bottom-up Heterointegration with Low-defects and Membrane Production with High-throughput

Abstract

Conventional epitaxy has significantly advanced the semiconductor industry, driving remarkable progress in various application fields such as electronics and optoelectronics. However, several limitations of epitaxial techniques have impeded the development of next-generation electronic and optoelectronic devices. These limitations encompass the absence of cost-effective methods for producing functional membranes with high throughput, the need to reduce the high costs of non-silicon semiconductor wafers, and the challenge of effectively integrating multiple functional semiconductor layers without detrimental effects from defects or interfacial states caused by lattice mismatch and disparate thermal expansion coefficients. In this thesis, novel epitaxy techniques and an in-depth investigation of their underlying principles are introduced to tackle these limitations inherent in conventional epitaxy techniques, thus paving the way for the production of high-quality epitaxial membranes as well as their heterogeneous integration in a cost-effective and high-throughput manner. Firstly, a unique mechanism of relaxing misfit strain in lattice-mismatched heteroepitaxial systems is observed through the implementation of remote heteroepitaxy, which involves the process of conducting heteroepitaxy on graphene-coated substrates. This approach facilitates spontaneous relaxation of misfit strain and reduction of misfit dislocations in epilayers due to the slippery graphene surface, while preserving the single-crystalline properties of the epilayers by the penetrated atomic potential from the substrate through the graphene layer. It provides a new pathway towards the heterogeneous integration of largely lattice-mismatched systems with minimized dislocation density, which could eventually broaden the material spectrum for advanced electronics and photonics. Subsequently, a high-throughput layer transfer technique based on remote epitaxy with directly grown two-dimensional (2D) materials on wafers as an interlayer is 3 presented. This approach enables a pristine amorphous 2D-on-wafer template for epitaxy, addressing issues of degraded or contaminated semiconductor wafer surfaces after standard 2D materials growth or transfer processes. Consequently, it enables a scheme to produce multiple freestanding membranes from a single wafer without sacrificial layer etching or wafer polishing. Moreover, atomic-precision exfoliation at the 2D interface allows wafer recycling for subsequent membrane production, with the potential for substantial cost reduction in manufacturing processes involving nonsilicon wafers. Additionally, we demonstrate remote epitaxy and nanopatterned epitaxy of InP, along with large-scale flexible membrane exfoliation and InP wafer recycling. By employing ultra-low temperature boron nitride growth, we successfully implement these advanced epitaxy and layer transfer techniques on InP substrate, despite its low dissociation temperature and weak ionicity. This approach paves the way for new opportunities in InP thin film-based optoelectronics and novel heterostructures at a significantly reduced cost. Lastly, we delve into intricacies of remote epitaxy by elucidating the respective roles and impacts of the substrate material, 2D layer, 2D-substrate interface, and epitaxial material for electrostatic coupling of these materials, which governs cohesive ordering and can lead to single-crystal epitaxy in the overlying film. By exploring various material systems and processing conditions, we demonstrate that the rules of remote epitaxy vary significantly depending on the ionicity of material systems as well as the 2D-substrate interface and the epitaxy environment. These studies lay the theoretical foundation for all of the novel epitaxy on 2D techniques investigated in this thesis.Ph.D