Different As desorption behaviour at step edges on InAs(001) and GaAs(001) surfaces

Using scanning tunnelling microscopy (STM) and reflection high-energy electron diffraction (RHEED), we compare the As desorption from (2 x 4) reconstructed InAs(001) and GaAs(001) surfaces prepared by molecular beam epitaxy (MBE) and annealed under ultrahigh vacuum conditions. In both cases the annealing procedure finally leads to a domain structure with group-III (Ga/In) and group-V(As) terminated areas. The STM images reveal a remarkably different As desorption behaviour at step edges. On the GaAs(001) surface, As desorption starts at step edges and gradually continues on the terraces, while on the InAs(001) surface, As first abruptly desorbs from the terraces but remains at the step edges. The residual As decorates the steps on both the upper and the lower terrace.