Brittle and ductile failure behaviors of single crystal silicon

From photo-voltaic solar cells to semiconductor devices and nanotechnology, silicon substrate is still one of the most extensively used materials because of its abundance and excellent mechanical stability and the potential to combine sensing elements and electronics. Thus, it is imperative to understand the failure behaviors of silicon on micro/nano levels to improve the mechanical reliability of silicon-based devices. While silicon is brittle in normal conditions, experimental evidence has shown that it exhibits ductile failure accompanying plastic deformation depending on temperature, strain rate, device size, and other input parameters. However, a complete understanding of the mechanisms leading to these different failure behaviors and their relations with input parameters remain unanswered. In the present work, atomic simulations based on energy minimization are used to unveil the fundamental atomic-scale mechanisms for two competing phenomena of slip deformation and crack propagation. A single crystal silicon model with an existing crack is tested in the mode-I fracture setting, using Stillinger-Weber and modified embedded atom model potentials. The test is conducted with various orientations. The local stress distribution near the crack tip is evaluated to determine the critical stresses for slip and crack propagation, respectively. The minimum energy path connecting the normal state and the deformed state is constructed to find the energy barrier and the atomic rearrangement during the deformation.