Scanning tunneling microscopy has been used to study the surface morphology of strainedIn1−xGaxAslayers (either 2% compressively or 2% tensilely strained forx=0.18orx=0.75,respectively) grown by molecular beam epitaxy on (001) InP substrate under cation-stabilized conditions. Under such growing conditions a smooth two-dimensional (2D) surface morphology is well preserved until the onset of plastic relaxation. This behavior is completely unlike the 2D/3D growth mode transition observed under As-stabilized conditions of growth. Along with the 2D growth mode stabilization, a step-edge smoothing is also observed. These results are assigned to a high value of step formation free energy on (4×2) reconstructed surfaces. The resultant increase in surface tension delays the onset of coherent 3D island formation beyond the onset of plastic relaxation and stabilizes 2D growth.