A Physics-Based Empirical Model for Ge Self Diffusion in Silicon Germanium Alloys

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We propose a physics-based model for the Ge diffusivity in SiGe and empirically fit the model to previously reported experimental results. The self-diffusivity of Ge can be given by: DGe=D0*exp(Sx)*exp(-E/kT) where x is the Ge concentration, E is the activation energy given by 3.85 eV, S is a measure of the vacancy disorder entropy given by 11.56, D0 is the pre-exponential factor given by 0.137 cm2/sec, k is the Boltzmann constant and T is the temperature. The given values offer the best match with the published experimental data. It has been well-established in the literature that self-diffusion in pure Ge is mediated only by vacancies. It has been also shown that Ge diffusion is dominated by a vacancy mechanism at low temperatures. Since the published data on Ge diffusivity are in most cases for experiments done at temperatures lower than 1050 ºC, therefore; the only dominant mechanism for the self-diffusion of Ge is the vacancy exchange mechanism. The new term modifying the regular diffusivity equation to relate the diffusivity to the change in Ge concentration is a consequence of the change in the point defects disorder entropy as a result of adding more Ge atoms to the SiGe system.

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Journal: TechConnect Briefs
Volume: 3, Nanotechnology 2008: Microsystems, Photonics, Sensors, Fluidics, Modeling, and Simulation – Technical Proceedings of the 2008 NSTI Nanotechnology Conference and Trade Show, Volume 3
Published: June 1, 2008
Pages: 583 - 585
Industry sectors: Advanced Materials & Manufacturing | Sensors, MEMS, Electronics
Topic: Informatics, Modeling & Simulation
ISBN: 978-1-4200-8505-1