Faceting of Equilibrium and Metastable Nano- and Micro- structures: A Phase-Field Model of Surface Diffusion Tackling Realistic Shapes

Fine tuning of crystal morphology is nowadays an important step for a large variety of applications, such as the performance improvement in cutting-edge electronic devices. However, full control over the different, sometimes competing phenomena, is far from trivial and has yet to be reached. Numerical simulations are precious in limiting the parameter space to be sampled in actual experiments when searching for the desired system morphology, and also in the design of future, innovative structures. Here, we present a phase-field (PF) model of surface diffusion [1], able to describe the morphological evolution by means of a real kinetic pathway, driven by the minimization of the surface energy. A convenient and general description of surface-energy anisotropy, allowing us to simulate faceting also in the “strong anisotropy” regime, is introduced [2] and several illustrative applications to semiconductor structures are described. Complex phenomena, involving even topological changes, can be readily tackled in the PF framework, and their occurrence in the processing of technology-relevant microstructures [3] is also shown as an example, demonstrating the predicting power of our approach. Finally, we discuss preliminary but encouraging results, revealing the possibility to extend our model including further key phenomena such as misfit-strain relaxation, anisotropic fluxes, and orientation-dependent growth velocity. 1] B. Li, J. Lowengrub, A. Rätz and A. Voigt. Commun. Comput. Phys. 6, 433 (2009). [2] M. Salvalaglio, R. Backofen, R. Bergamaschini, F. Montalenti and A. Voigt, Accepted, Cryst. Growth Des. 15, 2787 (2015). [3] C. V. Falub, H. von Känel, F. Isa, R. Bergamaschini, A. Marzegalli, D. Chrastina, G. Isella, E. Müller, P. Niedermann and L. Miglio. Science 335, 1330 (2012).