Author: Wu, Zehan
Title: Physical vapor deposition of elemental ultrathin films and heterostructures
Advisors: Hao, Jianhua (AP)
Degree: Ph.D.
Year: 2022
Subject: Physical vapor deposition
Thin films
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xxi, 162 pages : color illustrations
Language: English
Abstract: Two-dimensional (2D) materials are of high expectations to break through the physical limits in conventional silicon-based information industry. In addition, the 2D nature means the thinnest unsupported crystalline solid that can be realized, as well as the appealing intralayer transport of charges, heat, spin, or photons. In the 2D-material family, elemental 2D ultrathin layers have attracted great attentions recently to be the strongest candidates for semiconductor-channel applications in atomically thin level. Nevertheless, the large-scale synthesis is still a major limitation for their applications in information industry. In this regard, the physical vapor deposition (PVD) process, which is a method of replicating the chemical composition and structure from the source materials and achieving the lattice recombination under specific growth conditions, had been increasingly considered as a promising approach for the large-scale bottom-up synthesis of elemental and even more other 2D ultrathin layers. Furthermore, PVD approach had been widely accepted for the continuously in-situ fabrication of multiple-layer heterostructure with satisfactory interface, which is the most concerned and rapidly developing field in 2D materials research and applications.
In this thesis, the pulsed laser deposition (PLD) approach, one typical PVD method, was successfully employed for the centimetre-scale growth of group-VA elemental 2D ultrathin layers, and the further in-situ fabrication of van der Waals (vdW) heterostructures, in controllable way. The first achievement is the bottom-up synthesis of centimetre-scale few-layer 2D black phosphorus (BP). Through detailed manipulations on the experimental conditions of PLD, few-layer BP films with high crystalline quality and large-scale lattice homogeneity were grown on the 2D-surface of mica substrate, with controllable layer number ranging from 1 to 10 and horizontal area beyond 1 cm2. In addition, BP-based centimetre-scale field-effect transistor (FET) arrays were also fabricated and showing attractive electrical performances, including appealing carrier-mobility up to 617 cm2V-1s-1 at 250 K, high current switching ratio more than 104, and large-scale uniformity and stability. In contrast to detached BP fragments fabricated under extreme experimental conditions in earlier reports, the continuously large-scale PLD growth of ultrathin BP layers provide great possibilities for future explorations in the scalable device arrays and integrated circuit systems in atomically thin level. Secondly, the layered 2D β-bismuth was also successfully grown into ultrathin layers with large-scale homogeneity and high crystalline-quality through the PLD approach. Next, it was further developed into a centimetre-scale vdW heterostructure of β-bismuth/ε-InSe through the in-situ multiple-PLD process. An electron-doping effect on the bottom ε-InSe layers when encountering the top β-bismuth layers was evidenced by X-ray/ultraviolet photoelectron spectroscopy and Raman spectroscopy, which is of high expectations on tuning the electrical characteristics of ε-InSe layers and developing large-scale device arrays and integrated systems in high performance based on this PLD-grown heterostructure.
To sum up, the centimeter-scale bottom-up PVD growth of two group-VA elemental 2D ultrathin layers, BP, and β-bismuth, as well as a further developed vdW heterostructure of β-bismuth/ε-InSe, were demonstrated in this thesis. On these bases, advanced scalable-electronic applications and integrated-circuit systems can be designed and fabricated, setting a crucial stage for laying the foundation of 2D materials to future information industry.
Rights: All rights reserved
Access: open access

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