The α-fringe contrast of thin twins in relation to the anomalous weak-beam contrast of stacking faults

The α-fringe contrast exhibited by microtwins of varied thickness in (001) oriented Cd0.96Zn0.04Te is characterised for both strong- and weak-beam conditions. It is demonstrated that the contrast behaviour allows the form of the twin to be determined as a function of its thickness. If N is the number of (111) planes in the twin then the three distinct classes of contrast behaviour exhibited are associated with the twin being “intrinsic” (N = 3n + 1), “extrinsic” (N = 3n − 1) or “perfect” (N = 3n). It is shown that care is required to distinguish intrinsic and extrinsic faults from their twin counterparts and further examples of twins that might have been taken to be faults without full characterisation of their contrast are described in a crept γγ′ alloy. It is noted that the common presence of such defects is of relevance in the modelling both of the growth of compound semiconductors and of the mechanisms involved in creep. The implications of the similarity of microtwin and fault contrast are also discussed in relation to the literature on the “anomalous” weak-beam contrast of stacking faults.