Structural investigation of MOVPE grown InGaAs buffer layers

We have used X-ray diffraction to study the residual elastic strain in InxGa1 - xAs (0.07 < x < 0.14) layers grown by MOVPE on GaAs substrate, as a function of growth conditions, growth procedures and post-growth treatment. The samples have been grown at temperatures ranging from 625 degrees C to 680 degrees C with a growth rate between 0.45 and 2 mu m/h. For thick layers, the residual elastic strain represents about 15% of the initial lattice mismatch and is independent of the Indium composition. The extent of strain relief is not significantly changed by an increase in growth temperature from 625 degrees C to 680 degrees C. On the other hand, we found that the extent of strain relief is dependant upon the growth rate. The residual strain can be reduced to 5% of the lattice mismatch by lowering the growth rate from 1 to 0.45 mu m/h. This variation is related to the increased time at which the structure is at the growth temperature, since a post-growth annealing for one hour at growth temperature of a sample grown at 1 mu m/h leads also to the same reduction of the residual strain. Due to dislocations interactions, the effective stress responsible for dislocations motion and consequently the dislocation gliding velocity are significantly reduced. In these conditions, the time required by a dislocation to glide to the interface is comparable to the growth time.