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.
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.
Today, much is still to be done to explore and fully unleash the potential of this brand-new class of intriguing materials and devices. Modeling and simulations are essential at this stage to orient the field and guide experimentalists. One of the fundamental challenge to be addressed is to understand how these 2D materials can be contacted to 3D metals to allow good quality, or ohmic, contact for the devices. Typically, today, highly resistive contacts related to high interfacial Schottky barriers with values that are not in agreement with the standard theory are measured experimentally. This severely hampers the performance and potential for application of 2D transistors. The transport through metal – 2D semiconductor interfaces is complicated by the absence of strong bond between the metal and the 2D material in the third dimension.
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, to understand and explore the complicated metal – 2D interface, a First principle atomistic method, such as Density-Functional-Theory (DFT), is indispensable. 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 material devices, focusing on the modeling and physical understanding of the role of the metal - semiconductor interface in the overall transport properties. These include monolayer or a few layers of semiconducting mono- or heterojunction materials with various semiconducting – metal interfaces... You will build, using DFT, 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.
Type of project: Internship, Thesis, Combination of internship and thesis
Duration: 6 -12 month
Required degree: Master of Science, Master of Engineering Science
Required background: Electrotechnics/Electrical Engineering, Nanoscience & Nanotechnology, Physics
Supervising scientist(s): For further information or for application, please contact: Aryan Afzalian (Aryan.Afzalian@imec.be)
Only for self-supporting students