GaAs(311) surfaces grown by molecular beam epitaxy are investigated by in situ ultrahigh-vacuum scanning tunnelling microscopy. The observation of an atomically flat $\mathrm{Ga}(2\mathrm{}\times 1)$-reconstructed GaAs(311) surface and its transformation to a $8\times 1$-reconstructed GaAs(311) surface leads to an improved understanding of the processes involved in the step formation. The high density of steps observed on the $8\times 1$-reconstructed GaAs(311) surface along the $\left[2¯33\right]$ direction originates from the change of surface atomic density required to accommodate the surface transition from the $\mathrm{Ga}(2\mathrm{}\times 1)$ surface to the $8\times 1$ surface. This understanding is further supported by the observation of independent step formation.

• Received 27 August 2002

DOI:https://doi.org/10.1103/PhysRevB.66.193313