Surface diffusion and adatom stoichiometry in GaAs MBE studied by microprobe-RHEED/SEM MBE

The incorporation diffusion lenght of surface migrating adatoms, λinc, is studied theoretically and experimentally taking GaAs MBE as an example. By using microprobe-RHEED/SEM MBE equipment, it is demonstrated that λinc depends strongly on the As pressure and takes a value of the order of 1 μm. This behavior is explained by assuming that the Ga flux entering the step exceeds that of As. On the other hand, when the Ga flux entering the step is less than that of As, λinc decreases to take the value of step separation which is typically of the order of a few tens of nm. It is concluded that the balance of Ga and As fluxes entering the step edge governs the incorporation diffusion length of Ga.