PhD researcher on scalable, layer-controlled synthesis of 2D semiconductor films

Leuven - PhD
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More than two weeks ago
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Meeting the technology requirements for the next-generation semiconductor devices represents a formidable challenge which will require new device architectures and/or additional materials. In this context, two-dimensional materials, due to their ultra-thin body nature, are ideal candidates to further advance CMOS technology to smaller device dimensions. Graphene is one of the most representative 2D materials but its range of applicability is limited by the absence of a bandgap. Within the growing field of 2D material, transition metal dichalcogenides (TMDS, e.g. MoS2, WS2, WSe2 ...) are attracting increasing interest. They are layered crystals consisting of self-passivated molecular layers stacked together by weak van der Waals interactions. Differently to graphene, they have the advantage of being semiconductors, thus making them appealing for transistor applications. Noteworthy, TMDC exhibit a wide range of electronic properties (bandgap energy, carrier type, etc.) which depend on composition, thickness and structure. In addition to that, the absence of surface dangling bonds and the ability to isolate and manipulate single layers make TMDC ideal building blocks for the fabrication of artificial heterojunctions with atomically sharp interfaces and designed band alignment.  

The development of a scalable synthesis technique is an important fundamental step towards the development of a manufacturable technology. However, despite the intense research efforts towards controlled deposition of 2D materials, wafer-scale synthesis of high quality, uniform TMDC films remains a challenging issue. So far, charge transport in synthetic transition metal dichalcogenides is dominated by extrinsic factors such as impurities and structural defects (grain boundaries, dislocations, vacancies), leading to much lower mobility than the theoretical limit. The chemical vapor deposition (CVD) technique has shown great potential to generate large area TMDC. Nevertheless, controlling the number of layers (from single- to few layers) and the structural properties across the full wafer area are still major challenges.

We are interested in the growth of large area (wafer-scale) TMDC thin layers by chemical vapor deposition. The aim of this project is to provide more profound insights for the controllable synthesis of 2D TMDC and develop a generic predictive model based on empirical observations and thermodynamic calculations. Within the framework of this PhD project, the student is expected to:

  • study the impact of growth conditions and substrate (composition, crystallinity, morphology) on mass transport and nucleation mechanisms;
  • demonstrate the ability to precisely engineer the 2D material structure and its transport properties;
  • develop a comprehensive physical picture to explain transport phenomena;
  • provide a clear path towards intrinsic charge transport in 2D TMDC for future high-performance device applications.

Besides, understanding of the CVD mechanism of different TMDC will enable the creation of novel artificial 2D lattices and complex heterostructures with tunable structure and transport properties.

References:
[1] Controlled Sulfurization Process for the Synthesis of Large Area MoS2 Films and MoS2/WS2 Heterostructures, Adv. Mater. Interfaces, 3, 1500635, 2015
[2] Exploring atomic defects in molybdenum disulphide monolayers, Nature Communications 6, 6293, 2015
[3] Towards intrinsic charge transport in monolayer molybdenum disulfide by defect and interface engineering. Nat. Communications 5, 5290, 2015

Required background: physics, material engineering, material science, nanotechnology, chemistry

Type of work: 10% literature study, 15-30% modeling and technology study, 60-85% experimental work

Supervisor: Annelies Delabie

Daily advisor: Daniele Chiappe

The reference code for this PhD position is STS1712-45. Mention this reference code on your application form.

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