The relationship between the surface morphology and strain relaxation is explored in strained InxGa1−xAs layers grown on GaAs by molecular beam epitaxy.Insitulight scattering, detected simultaneously along [110] and [11¯0], reveals an asymmetric surface roughening which is consistent withexsituscanning force microscopy. Transmission electron microscopy shows that strain relaxation by misfit dislocation formation occurs before the surface roughening is detected, for In0.18Ga0.82As films grown at 490 °C. ©1995 American Institute of Physics.