Step structure on the GaAs(2 5 11) surface

GaAs samples off-oriented from (2 5 11) by 1° and 5.2° were prepared by molecular-beam epitaxy and characterised in situ by scanning tunneling microscopy. Terraces of the GaAs(2 5 11) surface are separated by steps along three characteristic directions [3 1 1̄], [4 5 3̄], and [2 3̄ 1] which are equivalent to the intersections of the (0 1 1), (1 1 3)A, and (1 1 1)A planes with the (2 5 11) plane, respectively. On the basis of atomically resolved step images, step models were developed and analyzed with help of the electron counting rule (ECR). Step bunches along [3 1 1̄] form (0 1 1) facets. According to the derived models the steps along [3 1 1̄] fulfill the ECR, whereas the steps along [4 5 3̄] violate it. Steps along [2 3̄ 1] violate the ECR as well, but may fulfill it over mesoscopic areas.