We report on Sb surfactant growth of InAs nanostructures on GaAs0.51Sb0.49 layers deposited on InP (001) and on (113)B oriented substrates. On the (001) orientation, the presence of Sb significantly favors the two-dimensional growth regime. Even after the deposition of 5 mono-layers of InAs, the epitaxial film remains flat and InAs/GaAs0.51Sb0.49 type-II quantum wells are achieved. On (113)B substrates, same growth runs resulted in formation of high density InAs islands. Microscopic studies show that wetting layer is missing on (113)B substrates, and thus, a Volmer- Weber growth mode is concluded. These different behaviors are attributed to the surface energy changes induced by Sb atoms on surface.