Onset of plasticity in InxGa1−xAs multilayers

Coherently strained InxGa1−xAs multilayers with zero net strain have been investigated in order to determine the influence of coherency strains on the yield stress. The deformation behaviour has been studied using both ex- and in situ nanoindentation and transmission electron microscopy. Nanoindentation showed that the pressure required for the onset of yield decreased with increasing coherency strain, consistent with previous work, while the hardness remained constant. Transmission electron microscopy revealed that deformation was more prevalent in one layer. Using these observations, a straightforward analysis has been developed in which the yield pressure of the multilayer is related to the onset of flow in the weaker layer determined by both its intrinsic yield pressure and coherency strains. This gives good agreement with the experimental observations and is consistent with the observations of the effects of internal stresses in films elsewhere in the literature.