Measurement of residual strain in InGaAs buffer layers

InxGa1−xAs layers have been grown with different indium compositions and thicknesses above the critical layer thickness and the extent of strain relaxation has been measured using high-resolution x-ray diffraction. Our results show that, in thick layers, the residual strain is dependent upon the lattice mismatch. In a range from 30 times up to 300 times the critical layer thickness, the residual strain represents about 15% of the lattice mismatch, regardless of the In composition. Comparison with published experimental data shows that the magnitude of the residual strain is difficult to predict and depends upon parameters which are yet to be identified. Our data also shows a different behavior for a sample with thickness 450 times the critical layer thickness where strain relaxation is almost complete. One possible explanation is a relaxation process which takes place during the growth of the structure, leading to a time dependent lattice mismatch.