Introduction of misfit dislocations into strained-layer GaAs/In_xGa_1–xAs/GaAs heterostructures by mechanical bending

The stability of strained-layer heterostructure lasers can be assessed by their response to stimuli for the introduction of dislocations. Three-point bending at elevated temperatures has been applied to GaAs/In_xGa_1−xAs/GaAs heterostructures to apply such a thermomechanical stimulus. In each case, the middle-layer thickness was below the critical thickness predicted by the Matthews–Blakeslee model, so that the pre-test structures were fully strained with no observed misfit dislocations. The tensile stress of 46.4 MPa produced during the tests resulted in the formation of 60° misfit dislocations whose configurations changed according to the alignment of the bending axis. For bending in the [110] orientation, the misfit dislocations formed parallel to each other and to the bending axis. For [100] bending, they formed an orthogonal pattern with each dislocation at 45° to the bending axis. In each case, these misfit dislocations caused relaxation of the strained-layer structures, even though the unloaded structures had been considered thermodynamically stable and the test temperatures were lower than those used during the original fabrication of the structures. These findings challenge existing assumptions of strained-layer stability and have implications for the design of lasers intended to be “buried and forgotten” in optical telecommunications.