Meeting the technology requirements for future semiconductor devices represents a formidable challenge which can be overcome by exploring novel device architectures and materials. In view of their ultra-thin body nature, two-dimensional materials are ideal candidates to further advance CMOS technology to smaller physical dimensions. The most representative 2D material, graphene, has limited applicability in this respect due to the absence of a bandgap. Transition metal dichalcogenides (MX2, with M a transition metal and X a chalcogen) such as molybdenum and tungsten disulfide (MoS2, WS2) do attract increasing interest as their electronic and optical properties can be tuned over a wide range . As such, a variety of applications with electronical, optical and sensing functions fall within reach of MX2 layers [1,2].
However, a key prerequisite to industrial exploitation of such disruptive materials is the availability of a manufacturable deposition approach for MX2. Ideally, the deposition technique should provide monolayer growth control and a highly crystalline structure uniformly across industry's standard 300mm wafer size. Despite exploration of various deposition approaches, the material quality remains immature as exemplified by poor electronic carrier mobility as compared to theoretical predictions [3-5]. Although metal-organic chemical vapor deposition (MOCVD) is widely accepted as the most promising deposition technique, fundamental understanding is lacking on how to design chemical deposition processes for MX2 layers, and control the morphologic and electronic properties of the deposited layers .
To address these challenges, the PhD project encompasses the following three research objectives:
- Portray and compare the growth and nucleation mechanism of MoS2 and WS2 during MOCVD based on analysis of the composition, structure and morphology of the deposited layers.
- From the obtained insight in the growth mechanism of MX2 layers, learn how to control the crystallinity and 2D structure, and evaluate how these physical properties impact the intrinsic electrical response
- Develop novel deposition concepts to precisely engineer the 2D material structure and show ultimate transport performance in line with the theoretical properties
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 precursors, and the starting surface on the composition, crystallinity, and morphology of the deposited layers through a suite of advanced and complementary characterization techniques (such as Rutherford Backscattering Spectroscopy, (conductive) atomic force microscopy). Based on these research objectives, the candidate will develop a methodology to carefully tune the 2D material structure, and benchmark the charge carrier transport properties of the deposited layers as compared to theoretical predictions .
 D. Akinwande, et al., Nature 2019, 573, 507;  M. Chhowalla, et al., Nat. Rev. Mater. 2016, 1, 16052;  J. Zheng, et al., Adv. Mater. 2017, 29, 1604540;  J. Jiang, et al., Chem. Soc. Rev., 2019, 48, 4639;  W. Zhang, et al, Nano Res. 2014, 7, 1731
Required background: Physics, Material engineering, Material science, Nanotechnology, Chemistry
Type of work: 20% literature study and theory, 80% experimental work
Supervisor: Annelies Delabie, ,
Daily advisor: Benjamin Groven
The reference code for this position is 2020-007. Mention this reference code on your application form.