/Exploit the properties of sapphire template to deposit monocrystalline MX2 monolayer for the next generation of field-effect transistors

Exploit the properties of sapphire template to deposit monocrystalline MX2 monolayer for the next generation of field-effect transistors

Leuven | More than two weeks ago

Exploring alternative sapphire planes to control the orientation of only three-atom-thick layers across 2-inch substrates at the forefront of semiconductor research

The semiconducting 2D transition metal dichalcogenides (MX2, with M - a transition metal and X - a chalcogen) such as molybdenum and tungsten disulfide (MoS2, WS2) are promising materials for future semiconductor devices [1]. The application of 2D materials in nano-electronic devices requires the availability of deposition techniques that provides monolayer growth control and a highly crystalline structure across a wafer. Currently, Chemical Vapor Deposition (CVD) is widely accepted as the most promising deposition technique for MX2 layers manufacturing [2].

In CVD growth, the choice of the starting substrate is of a primary importance. The substrate can act as a template that guides the crystallographic orientation of the growing film such that monocrystalline material can be obtained. Due to the lack of out-of-plane chemical bonding in a MX2 monolayer, the template and the 2D layer adhere via van der Waals forces. This growth mechanism is called van der Waals epitaxy.

Although monocrystalline c-plane sapphire is a conventional template for epitaxial MX2 growth, the six-fold crystal symmetry of both sapphire and the deposited MX2 monolayer impose several limitations. Literature predicts similar formation energy of MX2 crystal domains oriented along the same direction (0°) and the opposite direction (±60°). Hence, the crystal domains can exist in two orientations. Coalescence of domains oriented in the same direction may form large single-oriented regions, while coalescence of domains of opposite orientation introduces an antiphase boundary that degenerates the electrical properties of the film due to their metallic character.

In this Master project, we will investigate the growth of MX2 on alternative sapphire templates (e.g., sapphire a-, r-plane) with a lower surface symmetry compared to c-plane. By the reduction of substrate symmetry, we expect to promote the growth of material in one direction and to facilitate formation of monocrystalline 2D layer [3-4].The 2D layers are grown on up to 300 mm substrates using state-of-the-art 300 mm clean room facilities and research infrastructure. The candidate will study the impact of the starting surface on the essential mechanisms in CVD process, i.e., how the adsorption/diffusion mechanisms depend on surface energy of different sapphire planes. From this insight, we will deduce what is the impact of the template surface structure on crystallinity and morphology of the deposited layers. The candidate will form this understanding through a suite of advanced and complementary characterization techniques (such as Rutherford Backscattering Spectroscopy, (Conductive) Atomic Force Microscopy, Scanning Electron Microscopy, X-ray diffraction).


[1] D. Akinwande, et al., Nature 2019, 573, 507

[2] J. Jiang, et al., Chem. Soc. Rev., 2019, 48, 4639

[3] Ma, Z. P., Small, 2020, 16, 2000596

[4] J. Wang, Nat. Nanotechnol. 2022 17, 33–38

Type of project: Thesis

Duration: 1 year

Required degree: Master of Science, Master of Engineering Technology, Master of Engineering Science

Required background: Chemistry/Chemical Engineering, Materials Engineering, Nanoscience & Nanotechnology, Physics

Supervising scientist(s): For further information or for application, please contact: Annelies Delabie (Annelies.Delabie@imec.be) and Benjamin Groven (Benjamin.Groven@imec.be) and Iryna Kandybka (Iryna.Kandybka@imec.be)

Only for self-supporting students.

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