MULTIPLE DISLOCATION LOOPS IN LINEARLY GRADED INXGA1-XAS (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.53) ON GAAS AND INXGA1-XP (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.32) ON GAP

We report transmission electron microscopy studies of dislocation structures in two lattice-mismatched III-V systems, InxGa1-xAs (0 less-than-or-equal-to x less-than-or-equal-to 0.53)/GaAs and InxGa1-xP (0 less-than-or-equal-to x less-than-or-equal-to 0.32)/GaP, grown by gas-source molecular beam epitaxy. Multiple dislocation-loops, extending from within a linearly graded buffer layer to deep inside the substrate, were observed in both systems. All dislocations in each set of loops consisted of 60' dislocations with the same Burgers vector on a similar {111} glide plane. The density in the graded buffer and the substrate was estimated to be 2 X 10(9)/cm2, and their appearance was associated with low threading dislocation densities and good optical quality in material grown on top of the buffer layer, InP/In0.53Ga0;.47As on GaAs or In0.32Ga0.68P on GaP.