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We studied the misfit stress in CdTe(100)/GaAs(100). In general, this highly mismatched system initially forms a ‘‘coincidence interface,’’ where seven CdTe lattices match with eight GaAs lattices. In this system, the epilayer is elastically strained by the mismatch remaining between both groups of lattices. Afterward, the misfit stress is gradually relaxed with the generation of misfit dislocations. In this work, we derived a new model to describe this misfit relaxation mechanism and verified it with experimental observations. As introducing the effects of the interface modification, we found that the simple force balance between the substrate and epilayer governed the misfit stress. We assume that the relaxation process during growth is similar to that in CdTe/CdZnTe, since the residual misfit was fairly small. By extending the stress relaxation model of CdTe/GaAs, it is possible to explain the strain in CdTe/ZnTe/GaAs, which contains two highly mismatched interfaces. The threading dislocations in HgCdTe, derived from the CdTe buffer, decreased with increasing CdTe thickness. Assuming that the misfit dislocations are generated by bending threading dislocations, we could explain the dislocation reduction by utilizing the above misfit stress relaxation model. In spite of the extremely large mismatch, the structural quality of CdTe(100)/GaAs(100) was improved due to the relatively small strain remaining in the coincidence interface. © 1996 American Institute of Physics.