(222bk) Validation of An Empirical Interatomic Potential for the Si-Ge-O System: Application to Selective Epitaxial Growth of Ge On Si/SiO2

The fidelity of a Tersoff-based empirical potential model for the Ge-Si-O ternary atomic system [1,2] is studied in detail, with the ultimate aim of validating the potential for later use in large-scale simulations of Ge selective epitaxial growth (SEG) on crystalline silicon.  The ability to grow thin Ge films on bulk Si wafers is of interest as a cost-effective means of producing substrates for high-efficiency III-V multijunction photovoltaic devices.  In this context, SEG is a powerful approach for reducing the lattice and thermal expansion mismatch between two films of different materials that are epitaxially adhered.  In the process of force-field validation, several comparisons are presented between the predictions of atomistic simulations based on the empirical potential studied here and prior experimental measurements and electronic structure calculations.  The points of comparison include the structure and thermodynamics of bulk amorphous silica (a-SiO₂), the a-SiO₂ free surface, the c-Si/a-SiO₂ interface, the c-Ge/a-SiO₂ interface, and the desorption, wetting, and diffusion behavior of Ge atoms on a-SiO₂ surfaces.  A single fitting parameter, which describes the strength of the Ge-O interaction, is used to establish good agreement between the empirical potential predictions and experimental measurements across all points of comparison.  We conclude that a Tersoff-based empirical potential, while it neglects explicit Coulombic interactions and is highly simplified, is a reasonable basis for probing the Ge/SiO₂/Si material system.  The resulting potential is used to generate some predictions for the behavior of Ge island coalescence, which is known to lead to defect formation but has not yet been understood.

[1] J. Tersoff, Phys. Rev. B 39, 5566 (1989).

[2] S. Munetoh, T. Motooka, K. Moriguchi and A. Shintani, Comput. Mater. Sci 39, 334 (2007).