ON THE YIELD-POINT OF FLOATING-ZONE SILICON SINGLE-CRYSTALS .1. YIELD STRESSES AND ACTIVATION PARAMETERS

In initially dislocation-free silicon single crystals deformed in compression (single chip) at low strain rates, the lower yield stress tau //1//y exhibits a three-stage temperature dependence with a plateau (1170 K APP 1STH T APP 1STH 1320 K at gamma approximately equals 2 multiplied by 10** minus **5 s** minus **1) between the low- and high-temperature regimes, where tau //1//y decreases with increasing T. Pre-strained silicon crystals were deformed in the temperature range of dislocation velocity measurements (820 K APP 1STH T APP 1STH 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.