Effect of compressive strain relaxation on surface morphology in GaAsP growth on GaP substrate

► Compressive strain in GaAs0.6P0.4 grown on GaP substrate was relaxed by plane slips. ► Compressive strain in GaAs grown on GaP substrate was relaxed by formation of island structures. ► GaAs surface is much flatter than that of GaAsP. ► Controlling of strain relaxation mechanism is a method to achieve planar surfaces. ► Different relaxation methods were explained by critical thickness and transition thickness models.