[en] Mismatched InGaAs-GaAs epitaxial layers were grown by molecular beam epitaxy (MBE) on substrates containing 9800 or <100 dislocations/cm/sup 2/. Cathodoluminescence (CL), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), and energy dispersive x-ray analysis (EDX) were used to analyze the effect of mismatch and substrate dislocation density on interface morphology. Surface ridges in scanning electron microscopy (SEM) images were found to correlate with areas of high recombination in CL. The spacing of dark recombination lines seen in CL was found to be an order of magnitude larger than the spacing of misfit dislocations seen in TEM. CL/TEM correlation reveals that some areas of the misfit array act more strongly as recombination centers than others. CL of step etched samples show that interface defects propagate into the GaAs buffer layer to depths of 4000 A below the interface. The substrate dislocation density does not have a major effect on the number or spacing of the dark recombination lines