GALLIUM GROWTH AND RECONSTRUCTION ON THE SI(100) SURFACE

The behavior of gallium on the Si (100) 2X1 surface has been studied using scanning tunneling microscopy (STM) for metal coverages below one monolayer (ML). Below 0.5 ML, the Ga atoms form dimers that bond to the Si dimers, with the Ga dimers forming rows perpendicular to the underlying Si dimer rows. The Ga dimer rows form areas of 2 X 3 order for coverages below 0.3 ML and 2X2 order at 0.5 ML, in agreement with reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED) data. Ga growth is anisotropic at low coverages, forming areas covered by long 2x3 islands oriented parallel to the Ga dimer rows. When the surface exhibits mixed 2x3 and 2x2 ordering between 0.3 and 0.5 ML, the Ga dimers are strongly correlated along the rows, but the rows themselves are randomly spaced every two or three unit cells apart. Since all surface dangling bonds are saturated at 0.5 ML (2 X 2), a different bonding behavior is expected above 0.5 ML. For such coverages, STM results give evidence for Ga growth on the 2 X 2 Ga terminated surface with an (n X 8) ordering, where n usually equals 4 or 5. The detailed nature of this reconstruction is not yet known, but does not appear to involve Ga dimers. © 1990, American Vacuum Society. All rights reserved.