LUDERS BANDS IN DEFORMED SILICON-CRYSTALS

The formation of Lüders bands in Czochralski and float-zone silicon cŕystals, oriented for single slip, has been investigated at 800, 900 and 1000°C. At 800°C. Lüders strain is observed in Czochralski crystals, whereas the situation is ill-defined in the case of float-zone crystals. However, the Lüders deformation observed at 800°C can be eliminated by a double heat treatment consisting of a 4 h anneal at 700°C followed by a second anneal at 1000°C for 30 h. Furthermore, on increasing the deformation temperature, the tendency for Lüders deformation progressively decreases. Arguments, based on Hahn's postulates for nonuniform yielding, have been developed to rationalize the observed differences between Czochralski and float-zone crystals, influence of heat treatment and deformation temperature. The Lüders front is observed to lie close to the (1̄01) plane. Microstructures at and behind the front have been investigated by transmission electron microscopy. An explanation involving strain compatibility between the deformed and undeformed regions is presented to explain the observed crystallography. © 1979.