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

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

PhD - Leuven | More than two weeks ago

You will build fundamental understanding that contributes to the development of innovative and industrially relevant solutions for 2D material devices
Two-dimensional (2D) materials, with graphene as 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 [1,2]. 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 2D material surface complicates the formation of nm-thin insulating layers by ALD. In addition, because of their atomic scale thickness, the charge transport in 2D semiconductors depends to a large extend on the external surroundings. The interfaces and their stability during processing sequences will govern the electronic device functioning and performance.

The objective of this PhD project is to obtain insight into the mechanisms during 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 [3]. 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 2D material surface [4]. We will study these chemical and physical processes in-situ by characterization techniques like X-ray photo-electron spectroscopy and Atomic Force Microscopy, in imec’s new Materials and Interface (M&I) lab. Additional information about the growth evolution comes from ex-situ characterization techniques including Rutherford Backscattering spectrometry and Raman spectroscopy. We will explore ALD process modifications and functionalization approaches and insights will be used to design new deposition approaches to create nm-thin dielectric layers on 2D semiconductors. Finally, the properties of the deposited dielectric layers, the resulting interface with the 2D semiconductor and its performance in electrical devices will be tested in collaboration with the beyond CMOS team at imec.

Required background: Chemistry, Physics, Material science, Nanotechnology

Type of work: 10% literature, 90% experimental work

Supervisor: Annelies Delabie

Daily advisor: Daire Cott, Dennis Lin

The reference code for this position is 2021-071. Mention this reference code on your application form.

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