Development and application of first-principle based methods for the accurate calculation of electronic properties of defects in 2D semiconductors

• Applicant: Dr. Michael Lorke
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525065834

The exploding basic research on 2D semiconductors has pointed out the high potential of these sys-tems in many application areas, like micro/optoelectronics, photovoltaics/catalysis, and energy conversion/storage. Most of these require knowledge about defects which influence or facilitate device behavior. Electronic structure calculation of defects in 2D systems represents a new challenge for theoretical defect physics, because all known exchange functionals within density functional theory assumes homogeneous and isotropic screening, which is obviously not the case in layered systems. We have shown previously that accurate results for defects can only be obtained if the functional is Koopmans-compliant and reproduces the band gap. While this can be achieved by tuned semi-empirical hybrid functionals in the bulk, the same accuracy cannot be provided in a single layer, or – for that matter – on the surface of the bulk material, because of the inhomogeneity in the screening, induced by the presence of the interface. Earlier, we have developed a new exchange functional, which meets the required criteria by taking into account microscopic screening in bulk semiconduc-tors. In this project we want to extend this functional to inhomogeneous screening at interfaces, and we want to apply it to address a series of technologically relevant questions regarding defects in 2D systems. We will investigate how the number of layers affects the electronic activity of defects in few layer systems, how defects in the encapsulating monolayer or in the substrate affect the optical and electronic properties of the functional monolayer in Van-de-Waals heterostructures, and we will also address the equilibrium position of intrinsic defect and small polarons with respect to the sur-face, which is a critical question for photocatalysis. We will use many-body GW calculations (where possible) as well as direct comparison with experiment (in framework of a cooperation) for valida-tion. The project will provide predictions in a wide variety of systems involving hexagonal boron nitride, gallium selenide, tungsten- and molybdenum-dichalcogenides. The new functional developed here will also be of relevance to calculating electronic, optical, and catalytic properties of any layered semiconductor or any semiconductor surface.

• DFG Programme: Research Grants