On the yield point of floating-zone silicon single crystals II. A quantitative analysis of the dislocation structure at the lower yield point

Abstract

The dislocation structures in silicon single crystals deformed up to the lower yield point at moderate temperatures (823 K ≲ T ≲ 1073 K) and low shear strain rates (γ<2×10⁻⁴s⁻¹) were estimated by transmission electron microscopy. Both the total dislocation density ρ_t and the mobile-dislocation density ρ_m could be measured rather accurately, at least when the dislocations lie preferentially along ⟨110⟩ orientations. Local shear stresses were estimated from the radius of curvature at dislocation bends. With the distribution of local stresses and the known dislocation velocities, an average velocity v and the corresponding effective stress τ_eff could be derived. The internal consistency of the measured ρ_m and τ_eff was checked using Orowan's relation

where b is the Burgers vector, and was found to be good at sufficiently high stresses (τ_1y ≳ 10 MPa), giving support to the view that, in those conditions, τ_eff is probably much closer to τ_ly than predicted by current models.