Energy dependence of anisotropy of defect production in electron irradiated diamond?type crystals

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Abstract
Qualitative arguments are presented concerning relative rates of creation of point defects, under electron irradiation at various energies along ⟨111⟩⟨110⟩ and ⟨100⟩ directions, for a diamond-type lattice. A simple model is used in which displacements can occur only as a result of recoils close to ⟨111⟩ directions away from nearest neighbours, requiring a displacement energy E d111. The relative rates are governed by the number of such directions lying within the cone of recoil angles inside which the recoil energy exceeds E d111, and the differential cross section. With increasing energy, repeated changes in the order of the orientations with respect to displacement rate are predicted. Comparison with the experimental results on Si in Part I shows that all the features predicted are seen apart from one not expected in this energy range; avalue of 22 ev is obtained for E d111. Published measurements on Ge also appear to support the model.