Mg ordering, reaction, and crystallite formation on GaAs(110): Scanning tunneling microscopy and photoemission studies

The coverage-dependent growth structures formed by Mg deposition on GaAs(110) have been studied using scanning tunneling microscopy (STM) and synchrotron-radiation photoemission. In the low-coverage regime at 300 K, Mg adatoms bond on a bridge site between one Ga and two As surface atoms to form two-dimensional domains with local 2×{}1 structure. Dual-bias STM imaging shows a higher density of unoccupied states than occupied states for these Mg atoms, indicating charge transfer from Mg to the substrate. This 2×{}1 overlayer is replaced by three-dimensional clusters when the local atom density increases and chemical intermixing is initiated. With increased Mg deposition, the heterogeneous surface region becomes more uniformly reacted and the clusters coalesce. By {~}10-monolayer deposition, the resulting polycrystalline film is locally smooth, although atomic height steps are evident and there are a large number of dislocations.