Crystal Growth and Defect Structure of Zinc Sulfide and Zinc Selenide Platelets

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Abstract
An electron‐microscope study has been made of the growth of zinc sulfide and zinc selenide platelets from the vapor phase. One of the typical growth habits, corresponding to a thin plate parallel to (12̄10), was studied in detail. Many of the crystals are in the form of flat platelets, sawtoothed along one edge. The distribution of stacking faults in these crystals has several characteristic features related to the shape of the crystal. For example: (i) A stacking fault, near and parallel to the straight edge of the crystal, divides the crystal in two parts; one is almost defect‐free and the other contains many defects. (ii) There is a decrease in the number of stacking faults on moving away from the dividing stacking fault. (iii) The grooves on the ragged edge of the crystal are terminated by stacking faults. (iv) The stacking faults near the ragged edge are distributed roughly on lines perpendicular to the straight edge. These lines are directed to the grooves of the ragged edge. A possible model for the growth process of the platelets is discussed on the basis of these observations: Prior to the platelet formation, a whisker of wurtzite structure grows by an axial dislocation mechanism. The whisker broadens into a platelet by the two‐dimensional nucleation of the atomic steps on the surfaces. The process of the formation of the atomic steps and the shape of the crystal are discussed from the observed distribution of the stacking faults.