Growth of GaAs/GaAsSb heterostructure nanowires on silicon without the need for gold seed particles is presented. A high vertical yield of GaAs nanowires is first obtained, and then GaAsxSb1-x segments are successfully grown axially in these nanowires. GaAsSb can also be integrated as a shell around the GaAs core. Finally, two GaAsSb segments are grown inside a GaAs nanowire and passivated using an AlxGa1-xAs shell. It is found that no stacking faults or twin planes occur in the GaAsSb segments.