SURFACE-MORPHOLOGY OF MBE-GROWN GAAS(001)-(2X4) AND GAAS(001)-FACETED SURFACES INVESTIGATED BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy is used to study the morphology of nominally flat p-type (2 x 4)-reconstructed GaAs(001) and faceted n-type GaAs(001) surfaces. On the flat surfaces the effect of the MBE growth rate on the island structures was investigated. A detailed statistical analysis of the STM images of individual growths was performed to calculate the step-density and the step-length ratio of the islands. The density of the steps parallel to the dimers, A-type steps, is about twice the density of the steps perpendicular to the dimers, B-type steps. The length ratio of step A to step B was calculated to be 2.4:1. The images obtained on the faceted surface reveal predominantly a (2 x 4) local ordering. There is also an increased anisotropy in the local island shape in comparison to the flat surfaces.