On the yield point of floating-zone silicon single crystals

Abstract

In initially dislocation-free silicon single crystals deformed in compression (single slip) at low strain rates, the lower yield stress τ_1y exhibits a three-stage temperature dependence with a plateau (1170K ≲ T ≲ 1320 K at [ydot]≅ 2 × 10⁻⁵ s⁻¹) between the low- and high-temperature regimes, where τ_1y decreases with increasing T. Pre-strained silicon crystals were deformed in the temperature range of dislocation velocity measurements (820 K ≲ T ≲ 1070 K). With the assumption that pre-straining, which minimizes yield-point phenomena, ensures dislocation structures (i.e. internal stresses) that are at worst only weakly dependent on the deformation conditions, the activation Gibbs free energies derived from activation volumes measured at the lower yield point are found to be in very good agreement with activation energies for dislocation velocity at the same stresses.