Bridging first principles modelling with nanodevice TCAD simulations

Mattias Palsgaard

    Research output: Book/ReportPh.D. thesisResearch

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    Abstract

    This thesis is concerned with calculating the properties of electronic devices using first principles atomic scale methods. For this purpose, we develop new methods to extract important information from these calculations that can be included in device level simulations tools. The design of electronic devices is often supported by technology computer aided design (TCAD) tools. At the device level, TCAD models typically use continuum descriptions defining the constituent materials by parameters like effective masses and mobility. These parameters are typically measured in experiments or obtained from atomic-scale calculations of bulk crystals when no experiments are available.
    Atomic-scale phenomena like surface effects or interfaces are becoming more important than ever due to the continued miniaturization of electronics. As a result the bulk parameters used in device level TCAD simulations, in many cases, fail to accurately describe the properties of the electronic devices. In this thesis we use density functional theory (DFT) together with nonequilibrium Green’s function (NEGF) theory to accurately calculate transport at the atomic level. These calcualtions are non-emperical and can therefore be used to make prediction about devices using new promising materials. New methods to extract mobility and effective masses are developed including effects such as quantum confinement and coupling between electrons and quantized vibrations of the crystal lattice (phonons). The methods are tested against the current state-of-the-art and the resulting parameters are compared to those measured in experiments.
    We also carry out studies of several different thin-film solar cells including at the same time light-matter interactions and electron-phonon coupling. The current due to sunlight illumination is calculated either from device level TCAD simulations, including details from the atomic scale parametrically, or directly from atomic-scale DFT-NEGF transport calculations. Both methods show excellent agreement when compared to relevant experiments and offer new information useful for the optimization of these solar cells. We also find that an exciting, newly discovered twodimensional material opens up for the fabrication of atomically thin solar cells generating a substantial out-of-plane current. Several other promising device applications using this material are also found, including a record high homogeneous simultaneous p and n-type doping of graphene layers in close proximity.
    Original languageEnglish
    PublisherDTU Nanotech
    Number of pages190
    Publication statusPublished - 2018

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