Simulation and Electron Energy-Loss Spectroscopy of Electron Beam Induced Point Defect Agglomerations in Silicon
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Simulation and Electron Energy-Loss Spectroscopy of Electron Beam Induced Point Defect Agglomerations in Silicon Nathan G. Stoddard1, Gerd Duscher1,2, Wolfgang Windl3 and George A. Rozgonyi1 1.) Materials Science and Engineering Department, North Carolina State University, Raleigh, NC, 27695-7916 2.) Condensed Matter Science Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 3.) Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210-1178 ABSTRACT Nitrogen doped silicon samples were irradiated with 200 kV electrons in a transmission electron microscope (TEM). The resulting room temperature point defect creation, bonding and segregation were studied by in situ conventional and Z Contrast TEM imaging and electron energy loss spectroscopy (EELS). Energy loss spectra from areas attributed to be rich in vacancies or silicon self-interstitials are found to be significantly different from the bulk in the near-edge structure of their Si-L2,3 edges. The experimental results are compared with ab initio density of states calculations for electronically excited atoms near relaxed point defect structures and plans are outlined to extend this technique to individual point defect characterization. INTRODUCTION The study of point defects in semiconductors is a mature field, but one that still has much to reveal. Point defects play a central role in extended defect formation during crystal growth and are central to solid-state diffusion in semiconductors. Vacancies and self-interstitials are especially active at high temperatures, and their behavior in many ways influences the final properties of devices.[1] Extensive experimental and theoretical work has been applied to determining the structural configurations of point defects as well as their formation and activation energies.[2,3,4,5] The thorough application of ab initio atomic simulations have produced a wealth of insights into the interactions of dopants and point defects and experimental techniques like Fourier Transform of Infrared (FTIR) and electron paramagnetic resonance (EPR) can provide useful comparison points. Nevertheless, there is no way to image or in any way spatially resolve individual point defects or complexes of a few point defects, so matching experimental to theoretical data has remained somewhat elusive. Electron energy loss spectroscopy is an excellent tool for determining qualitative and quantitative chemical data with high spatial resolution. Absorption edges arise in the energy loss spectra due to excitations of core electrons whose energy is characteristic of its parent element.[6] The exact position of the edge can provide information on shifts in the energy of core levels or the electronic bands, while the shape of the edge reflects local bonding properties and the area under an edge is proportional to the relative concentration of that element.[7] It has been shown that the energy-loss near-edge structure (ELNES) can be simulated by calculating the angular
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momentum-resolved density
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