Difference in the Mechanical Strengths of Dislocation-Free Crystals of Czochralski Silicon and Float-Zone Silicon

The mechanical behaviors of dislocation-free crystals of Czochralski silicon and float-zone silicon are investigated as functions of the surface condition and the stressing rate. No difference in the yield strength is observed between the two types of crystals with chemically polished surfaces. On the other hand, the yield stress is measured to be higher for Czochralski crystals than for float-zone crystals at low stressing rates when the surfaces are abraded with carborundum. The results are interpreted in terms of the locking effect of dislocations by oxygen atoms.