Mechanism of twinning in zincblende structure crystals: New insights on polarity effects from a study of magnetic liquid encapsulated Czochralski grown InP single crystals

Synchrotron White Beam X-ray Topography (SWBXT) and synchrotron X-ray anomalous scattering have been employed to determine the polarity of {111} edge facets, anchored to the three phase boundary (TPB) on which twinning is observed to nucleate in Magnetic Liquid Encapsulated Czochralski (MLEC) grown sulfur doped, <001> InP single crystals. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on {1̄1̄1̄}_p faces. Of the four possible sets of edge facets, belonging to the {1̄1̄1̄}_p form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two can give rise to a {115} to {1̄1̄1̄}_p external shoulder facet conversion upon twinning, while the other two can give rise to a {114} to {110} conversion. For these cases, twinning is only observed when the {l̄1̄1̄}_p edge facets are anchored to the TPB in a region where the shoulder angle is close to 74.21° or 70.53°, facilitating the production of the {115} and {114} external shoulder facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.