STEP STRUCTURES AND TERRACE WIDTH ORDERING OF MOLECULAR-BEAM EPITAXIALLY GROWN GAAS-SURFACES OBSERVED BY SCANNING TUNNELING MICROSCOPY

We have observed the surface structures of molecular beam epitaxially (MBE) grown 30-monolayer (ML) GaAs on vicinal (001) surfaces using a multichamber ultrahigh-vacuum scanning tunneling microscope (STM). Only A-type step edges (parallel to the [110BAR] direction) were found in the STM images of vicinal surfaces cut toward [111]A (A-surface). Not only B-type step edges (parallel to the [110] direction), but also A-type step edges were observed on vicinal surfaces cut toward [111]B (B-surface); that is, wide terraces bordered by B-type step edges and narrow terraces bordered by A-type step edges co-existed on the B-surfaces. The B-surface structure is, thus, less uniform than that of the A-surface. We performed further MBE growth on the nonuniform B-surface under the step-flow condition. The surface structure evolved to be more uniform with growth.