Structure transition between two GaAs(0 0 1)-c(4×4) surface reconstructions in As4 flux

We have investigated the c(4×4) surface reconstructions of GaAs(0 0 1) using scanning tunneling microscopy. We found that, by the As4 flux in molecular beam epitaxy, the Ga–As dimer (c(4×4)α) and the As–As dimer (c(4×4)β) structures at the top of the surfaces are distinguished depending on the growth temperature and annealing time. Annealing for more than 2 h at 350 °C is required to obtain a stable c(4×4)β surface reconstruction dominantly under the As4 flux conditions. Furthermore, the Ga atoms in the c(4×4)α Ga–As heterodimers are segregated onto the surface and migrate to the step edges with the step barrier formation by the transition from α to β phases with decreasing annealing temperature.