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Defects in silicon: revisiting theoretical frameworks to guide ab initio characterization

Gabriela Herrero-Saboya 1, 2
1 LAAS-M3 - Équipe Modélisation Multi-niveaux des Matériaux
LAAS - Laboratoire d'analyse et d'architecture des systèmes
2 LAAS-MPN - Équipe Matériaux et Procédés pour la Nanoélectronique
LAAS - Laboratoire d'analyse et d'architecture des systèmes
Abstract : In this thesis, we describe the effect of localized defects on the electronic properties of silicon. After 60 years of silicon devices production, one might expect all details of this material to be fully understood, especially considering that the manufacture of nowadays nanometer-sized transistors requires quasi-atomic accuracy. However, as a direct result of such extreme miniaturization, the accidental creation of even one single trapping center can be sufficient to alter the desired electronic properties of the sample, becoming one of the most feared phenomena in the industry. Since the early years, the identification of these centers has been possible through the development of characterization techniques, capable of targeting specific defect properties, related to the position of the center-induced states within the semiconductor gap (infrared optical absorption, DLTS spectroscopy) or to the atomic distortions triggered by the form of the localized electronic density (EPR spectroscopy). Such collection of experimental data motivated the development of simple symmetry-based models, qualitatively reproducing the basic features of defects. The later exponential increase in computational power made ab-initio calculations the perfect candidate to give a quantitative theoretical model of point-defects in semiconductors. Atomistic numerical simulations in silicon, based on the Density Functional Theory, do however typically target specific defect-properties, not giving a complete theoretical picture of the system, often overlooking previous models and experimental evidence. In the present thesis, we provide new insight into iconic defects in silicon through the quantification of long-established atomistic models, making an explicit link with the characterization techniques. Our detailed exploration of the DFT energy surface of the silicon E-center, guided by a simple Jahn-Teller model, confirmed the observed defect-dynamics at different temperature regimes, allowing us to link the presence of such point-like defect to a burst noise in image sensors. Moreover, we investigate the hypothesis of enhancing photon-absorption in titanium-doped silicon solar cells by describing many-body effects in the form of the GW approximation, assigning the charged electronic excitations to transitions between Ti-related states, previously depicted by a phenomenological model for transition metals in silicon. We also propose a generalization of the preexisting toy-models to tackle complex centers, for which a notorious controversy within the ab-initio community still exists, showing explicitly the limitations of mean-field approaches when targeting highly localized electronic densities. We conclude with a brief critical review of the theoretical characterization of the defects electronic activity, and in particular the capture cross section of non-radiative transitions.
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Submitted on : Thursday, March 4, 2021 - 8:32:56 AM
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Gabriela Herrero-Saboya. Defects in silicon: revisiting theoretical frameworks to guide ab initio characterization. Micro and nanotechnologies/Microelectronics. Université Toulouse 3 Paul Sabatier (UT3 Paul Sabatier), 2020. English. ⟨NNT : 2020TOU30239⟩. ⟨tel-03215768v1⟩

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