Influence of growth conditions on the residual strain in thick metalorganic vapor phase epitaxy grown InGaAs epilayers

Abstract

The residual elastic strain has been measured in thick (≈2 μm) InxGa1−xAs (0.07<x<0.14) layers grown on GaAs substrates at a temperature of 625 °C and a growth rate of 1μm/h. X-ray diffraction experiments show that the residual strain represents 15% of the lattice mismatch. This result cannot be explained by the difference in thermal expansion coefficients between the substrate and epilayer, but can be qualitatively explained by a reduction of the effective stress due to repulsive interaction between dislocations. The effects of growth conditions on the extent of strain relief have also been studied and it was found that increasing the growth temperature from 625 to 670 and 680 °C does not significantly change the residual strain. On the other hand, the residual strain can be reduced to 5% or increased to 33% of the lattice mismatch by lowering the growth rate from 1 to 0.45 μm/h or by increasing the growth rate from 1 to 2 μm/h, respectively. This change is related to the variation of the growth time, since a post-growth anneal for 1 h at growth temperature of a sample grown at 1 μm/h leads also to the same reduction of the residual strain as when grown at lower rates. This shows that for thick layers, the relaxation process is not completed when the growth is interrupted and suggests that despite the strong reduction of the effective stress, the dislocations are still mobile.