Spontaneous appearance of high index facets during the evolution of step bunching on vicinal GaAs(001)

The evolution of step bunching on vicinal GaAs(001) annealed at different temperatures in AsH3 and H2 ambient was studied by scanning tunneling microscopy. The results provided aspects of the evolution of step bunching from the initial to the final stage. We observed a appearance of additional step bunchings which have a peculiar azimuth of 〈210〉, 〈210〉, 〈310〉, and 〈310〉.