Ab-Initio simulations of next-generation devices made of 2d or topological-insulator materials

Leuven - PhD
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Meer dan twee weken geleden

Explore and unleash the potential of a brand-new class of intriguing materials and devices, while learning to use and develop state-of-the-art quantum transport atomistic tools and methods.

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The discovery of graphene in 2004 has sparked a renewed interest for materials in 2-D form. Among other materials, transition metal dichalcogenides (TMDs) or black phosphorus (BP) are widely investigated by the scientific community for various applications such as sensing, lighting, and CMOS logic. Some of these 2-D materials also features intriguing new quantum states of matter, like the appearance of topologically protected states in topological insulator (TI) materials.

The large variety of 2-D materials with various bandgaps, effective masses, and their excellent electrostatic properties related to their atomistically thin 2-D nature hold promise to find in their midst the ultimate candidate for CMOS scaling, i.e., for transistors with a gate length, L, well below 10 nm. This include MOSFETs transistors but also novel devices, e.g., Tunnel-FETs than can be realized using a homojunction of an appropriate material or using a Van-der-Waals heterojunction layer stack, or even more advanced concepts using TI unique properties.

Today, much is still to be done to explore and fully unleash the potential of this brand-new class of intriguing materials and devices. One of the fundamental question is simply which 2-D material for which application. Modeling and simulation are essential at this stage to orient the field, guide experimentalist and help answer this question.

Atomistic full-band quantum transport simulations including electron-phonon scattering have been shown indispensable to consider intricate band-structure and transport effects, as for example narrow valleys and the need for phonon mediated transport in a MoS2 transistor and assess the performance of these devices. In addition, as there are many 2-D materials to explore on which not much is known, a parameter-free or Ab-Initio atomistic method, such as Density-Functional-Theory (DFT), is best. A state-of-the art simulator for 2-D material based devices uses a dissipative localized-orbital-basis Ab-Initio Atomistic NEGF algorithm. We have built such a simulator. The device Hamiltonian is created in our simulator using as building blocks DFT supercell elements of the materials or combination of materials of interest (e.g., computed by VASP or QUANTUM EXPRESSO) and transformed in a localized orbital-basis, as needed for transport, using the maximally-localized Wannier-function method.

In this thesis, you will explore the properties of new 2-D and TI materials. These include monolayer or a few layers of semiconducting mono- or heterojunction materials, semiconducting – metal interfaces... The materials can be pristine or include defects. You will build, using DFT and Wannier, the supercell elements needed for the device simulations. You will learn to use and develop, as needed, the most advanced quantum transport atomistic tools and methods. You will investigate the fundamental physics and performances of innovative devices. You will learn and benefit from the support from experts in the field. Possibility to closely work and interact with experimentalists is also available, as IMEC has a strong expertise in 2-D materials and devices fabrication and characterization.


Required background: Physical/Electrical/Electronic/Material Engineering or Physics

Type of work: ~50% NEGF device physics and simulations, ~30% quantum transport code development, ~20% DFT simulation of new material (2D, TI).

Supervisor: Michel Houssa, Aryan Afzalian

Daily advisor: Aryan Afzalian

The reference code for this position is 1812-44. Mention this reference code on your application form.

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