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Recent work has shown that the primary cause of rapid degradation in GaAs-(GaAl)As lasers is the propagation of dark-line defects which originate at threading dislocations present in the as-grown material. This paper considers the effect of first-order elastic interactions between dislocations and deliberately added impurities, such as the commonly used dopants and group III or V impurities. Strongly interacting impurities tend to concentrate preferentially around dislocations in positions where they relieve stress, thus forming an impurity cloud. Subsequent movement of the dislocation then becomes energetically unfavorable. For impurities such as In, Sb, and N the pinning forces can be as large as 1010dynes/cm2. It seems likely that this type of dislocation pinning can be used to eliminate or greatly reduce the probability of a threading dislocation initiating a dark-line defect.