Orientation dependence of the elastic instability on strained SiGe films

At low strain, SiGe films on Si substrates undergo the Asaro–Tiller–Grinfeld morphological instability. We demonstrate experimentally that this instability develops on Si(001) but not on Si(111) even after long annealing. Using a continuum description of surface diffusion in presence of wetting, elasticity, and surface energy anisotropy, we find a retardation of the instability on Si(111) due to a strong dependence of the instability onset as function of the surface stiffness. This retardation is at the origin of the inhibition of the instability on experimental time scales even after long annealing.