Growth-twinning in zincblende crystals: further insights from studies of liquid encapsulated Czochralski (LEC) grown InP single crystals

Synchrotron white beam X-ray topography (SWBXT) combined with chemical etching and Nomarski optical microscopy have been employed to investigate the phenomenon of twinning in sulfur doped, LEC grown <100> InP single crystals. Results confirm the general prediction of Hurle that twins nucleate in regions where {111} edge facets are anchored to the three phase boundary (TPB), and that twinning produces a {111} external facet on the shoulder region of the crystal. However, some specific aspects of Hurle's theory were corrected by this experimental study. A detailed X-ray examination revealed the appearance of a {115} external shoulder facet immediately before the occurrence of twinning. The location at which the twin nucleates is the point where the {115} shoulder facet is converted to a {111} external shoulder facet. This twinning mechanism allows for a reduction in free energy by converting the facet from a {115} to a {111} plane.