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

The polarity of {1 1 1} edge facets, anchored to the three-phase boundary (TPB), which give rise to growth-twin nucleation in the shoulder region of a [0 0 1], S-doped, magnetic liquid encapsulated Czochralski (MLEC) grown, InP boule, has been studied by chemical etching and synchrotron X-ray anomalous scattering. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on {1̄ 1̄ 1̄}_P faces. Of the four possible sets of edge facets, belonging to the {1̄ 1̄ 1̄}_P form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two of them can give rise to the conversion of a {1 1 5} external shoulder facet to a {1̄ 1̄ 1̄}_P one upon twinning, while the other two can give rise to the conversion of a {1 14} external shoulder facet to a {1 1 0} one. In both cases, twinning is only observed when the {1̄ 1̄ 1̄}_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 {1 1 5} and {1 1 4} external shoulder facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.