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

Abstract

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\ifmmode\times\else\texttimes\fi{}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\ifmmode\times\else\texttimes\fi{}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 \ensuremath{\sim}10-monolayer deposition, the resulting polycrystalline film is locally smooth, although atomic height steps are evident and there are a large number of dislocations.