On the yield point of floating-zone silicon single crystals III. The evolution of the dislocation structure through the yield point at low temperature

Abstract

The dislocation structures in silicon single crystals deformed up to different points in the yield region, at 823 K and at the shear strain rate γ of 2 × 10⁻⁵ s⁻¹, have been estimated by transmission electron microscopy. In addition to the total dislocation density ρ_t, the mobile dislocation density ρ_m can be measured with reasonable accuracy, thanks to the characteristic shape of dislocation loops. Local shear stresses are estimated from the radius of curvature at dislocation bends. Estimation of the effective stress τ_eff is difficult before the lower yield point because of micro-scale inhomogeneities. The internal consistency of the measured τ_eff and ρ has been checked using Orowan's relation, leading to the conclusion that, in the experimental conditions realized, τ_eff is very close to the applied stress and nearly all dislocations are mobile from the onset of plastic deformation up to the lower yield point.