Numerical investigation of the effects of phosphorus on the mechanical responses of [1 1 0]-oriented silicon nano-wires

The mechanism that phosphorus (P) impurities, one of the most commonly used impurities in silicon (Si), affect the tensile mechanical responses of [1 1 0]-Si nano-wires (NWs) is investigated using molecular dynamics (MD) with a Modified Embedded Atom Method (MEAM) potential. Tensile tests at 300 K are carried out for unnotched and notched Si NWs. For unnotched cases, P impurities randomly replace Si atoms at specific concentrations. Two patterns are considered for notched models, one undoped and one with doped notch tip. Results show that evenly distributed P impurities introduce an overall decrement in fracture strength of unnotched Si NWs as the concentration increases. The failure manner is that the local defects come into being around P, then rapidly nucleate and propagate, finally lead to fracture. However, for notched models, P can evidently enhance the fracture strength by impeding the cracking and growth of pre-existing cracks. With regard to Si NWs with surface defects exposed to strain, fracture usually starts from surface owing to stress concentration, indicating that P functions more critically on surface, especially near crack tips. Hopefully, this finding can be applied in the reliability design of Si-based NW devices. Moreover, when doped with P or notched on surface, the transition of failure mode for 2 nm and 3 nm NWs can happen, namely from ductile to brittle.