The activation strain tensor: Nonhydrostatic stress effects on crystal-growth kinetics

The solid-phase epitaxial-growth rate of crystalline Si from the amorphous Si on the tensile side is greater than on the compressive side of elastically bent wafers, in marked contrast to the behavior observed under hydrostatic pressure. The phenomenology of an activation strain tensor, the nonhydrostatic analogue of the activation volume, is developed to characterize such measurements. The measurement permits us to characterize to first order the entire activation strain tensor for solid-phase epitaxy of Si(001): The transition state for this process involves an in-plane expansion and a contraction in the direction normal to the interface. Its symmetry is inconsistent with all proposed bulk point-defect mechanisms.