Transmission electron microscopy, high-resolution X-ray diffraction and Rutherford backscattering study of strain release in InGaAs/GaAs buffer layers

Strain release and dislocation distribution in InGaAs/GaAs double heterostructures, step-graded and linear-graded buffer layers have been studied. A higher misfit dislocation density at the inner interface between the InGaAs layer and the substrate was found in all the samples. This corresponded to a strain release of the inner ternary layers much larger than predicted by equilibrium theories. The residual parallel strain of the external layers as a function of their thickness was found to follow a curve approximately of slope -0.5, in agreement with previous investigations on single InGaAs layers. This result has been interpreted as evidence that the elastic energy per unit interface area remains constant during the epilayer growth. The presence of numerous single and multiple dislocation loops inside the substrate was attributed to the strain relaxation occurring through dislocation multiplication via Frank-Read sources activated during the growth. A comparison with InGaAs/GaAs step-graded and linear-graded heterostructures is also shown and briefly discussed.