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 {(1) over bar (1) over bar (1) over bar}(P) faces. Of the four possible sets of edge facets, belonging to the {(1) over bar (1) over bar (1) over bar}(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 {(1) over bar (1) over bar (1) over bar}(P) one upon twinning, while the other two can give rise to the conversion of a {1 1 4} external shoulder facet to a {1 1 0} one. In both cases, twinning is only observed when the {(1) over bar (1) over bar (1) over bar}(P) edge facets are anchored to the TPB, in a region where the shoulder angle is close to 74.21 or 70.53 degrees, 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. (C) 1998 Elsevier Science B.V. All rights reserved.