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Project

Creating dielectric layers on two-dimensional (2D) semiconductors: chemical and physical mechanisms

Two-dimensional (2D) materials, with graphene as the most famous representative, are an interesting class of materials due to their ultra-thin body nature. inorganic 2D materials can exhibit either insulating, metallic, semi-metallic, or semiconducting properties, depending on the composition and structure. The semiconducting 2D materials like WS2 and MoS2 attract great interest for application in nano-electronic devices, in view of their monolayer thickness, large band gap values, low dielectric constants, structural stability, and self-passivating nature of the basal plane. One of the challenges for implementation in devices is creating the nm-thin insulating layers on the 2D semiconductor. Atomic Layer Deposition (ALD) has been widely used for the deposition of ultrathin gate dielectric films, as it can provide atomic-level growth control based on self-limiting surface reactions. However, the inherent self-passivated nature of the 2D material surface complicates the formation of the nm0-thin insulating layers by the ALD. In addition, because of their atomic-scale thickness, the charge transport in 2D semiconductors depends to a large extent on the external surroundings. The interfaces and their stability during processing sequences will govern the electronic device's functioning and performance. The objective of this Ph.D. project is to obtain insight into the mechanisms during the deposition of dielectrics (e.g. Al2O3, HfO2, ZrO2 ...) onto 2D semiconductor surfaces. The initial growth mechanism during ALD is governed by several processes, including adsorption of precursors, surface reactions, diffusion and aggregation. The interplay of these processes can become complex especially for deposition on 2D semiconductors, as the initial interactions between the 2D material surface and precursors are weak due to the inherent self-passivated nature of the 2D material surface. The chemical and physical processes will be studied in-situ by characterization techniques like x-ray photoelectron spectroscopy and Atomic Force Microscopy. Additional information about the growth evolution comes from ex-situ characterization techniques including Rutherford Backscattering spectrometry and Raman spectroscopy. ALD process modifications and functionalization approaches will also be explored to design new deposition approaches to create nm-thin dielectric layers on 2D semiconductors. Finally, the properties of the created dielectric layers, the resulting interface with the 2D semiconductor, and its performance in electrical devices will be tested.

Date:18 Jan 2022 →  Today
Keywords:Atomic Layer Deposition, 2D semiconductors, 2D materials, Thin Films, Dielectric Layers, Dielectrics
Disciplines:Dielectrics, piezoelectrics and ferroelectrics, Semiconductors and semimetals, Surfaces, interfaces, 2D materials, Nanofabrication, growth and self assembly, Nanomaterials, Nanoscale characterisation
Project type:PhD project