Microstructure and strain relaxation in organometallic vapor phase epitaxy of strain-compensated GaInP/InAsP multilayers on InP(001)

The various mechanisms responsible for the strain relaxation of strain-compensated GaInP/InAsP multilayers grown on InP(001) using low-pressure organometallic vapor-phase epitaxy (LP-OMVPE) were investigated using a combination of transmission electron microscopy (TEM), high-resolution x-ray diffraction (HRXRD), and reciprocal lattice mapping. We examined separately the effect of the misfit strain f as well as the total strain energy εT on the strain relaxation mechanisms. We also investigated the effect of the growth temperature Ts on roughening. For the structures composed of a small number of superlattice periods, N=10, TEM and HRXRD indicate that strain relaxation occurs essentially through non-homogeneities at the interfaces for increasing misfit strain f values (at least up to |f|=1%, the largest strain used in these experiments). In comparison, when the magnitude of the misfit strain is kept constant, increasing the number of periods eventually leads to a massive generation of dislocations in the multilayer. For |f|=0.75%, coherency breakdown was observed around the 14th–15th period in a 50-period sample. However, the strain-compensated multilayer structures can be in a metastable state since all layers are perfectly flat and no dislocations are visible in a 20-period sample with the same misfit strains in the layers. Finally, we observed that the growth temperature Ts had a drastic effect on the morphology of the layers: increasing Ts from 620 to 680 °C while keeping all other growth parameters constant introduced large periodic lateral thickness modulations as well as dislocation clusters in the structures. Diffraction contrast analysis in plan-view TEM indicates significant anisotropy with the features elongated in the [11̄0] direction. These results could be used as guidelines for the design of highly perfect and reliable device structures grown by LP-OMVPE.