Mechanisms of strain release in molecular-beam epitaxy-grown InGaAs/GaAs buffer heterostructures

Strain release and distribution in double InGaAs/GaAs heterostructure buffer layers were 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 which was much larger than that predicted by equilibrium theories. The residual parallel strain of the external layers as a function of the thickness was found to follow a curve of slope -0.502, in agreement with previous results on single InGaAs layers. These results were interpreted as evidence that the elastic energy per unit interface area remains constant during growth. The presence of numerous dislocation loops inside the substrate was considered to be responsible for the strain relaxation occurring through dislocation multiplication due to Frank-Read sources activated during growth. A comparison with InGaAs/GaAs step graded heterostructures is also discussed. Finally, lattice plane tilts between epilayers and substrates were found and attributed to the imbalance in the linear density of misfit dislocations with opposite components of the Burgers' vector (b(eff)(perpendicular to) perpendicular to the interface.