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 substrat e, as a function of growth conditions, growth procedures and post-grow th 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 de pendant 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 str ucture 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 al so to the same reduction of the residual strain. Due to dislocations i nteractions, the effective stress responsible for dislocations motion and consequently the dislocation gliding velocity are significantly re duced. In these conditions, the time required by a dislocation to glid e to the interface is comparable to the growth time.