DEFECT STRUCTURE OF GAAS(111)B (2X2) SURFACE OBSERVED BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopy (STM) and tunneling spectroscopic I-V me asurements of n-type GaAs(111)B (2 x 2) surfaces are reported. The sam ples grown by molecular beam epitaxy and the As-capping technique were employed to allow transfer into the ultrahigh vacuum scanning tunneli ng microscopy (UHV-STM) system. Filled and empty state images exhibit a hexagonal array of bright maxima spaced 8 angstrom apart consistent with the unit cell dimensions. The images show a variety of domain bou ndaries resulting from surface stacking faults. The domain boundaries are oriented along [101BAR], [011BAR], and [110BAR] directions. Numero us defects are observed at the point where these domain boundaries int ersect. Atomic models for these defects are shown. Scanning tunneling spectroscopic data indicate that the Fermi level on this surface is pi nned midgap.