Surface Migration of Ga and Al Atoms on (100) GaAs and AlAs during Migration-Enhanced Epitaxy

Adsorption and migration characteristics of Ga and Al atoms on the GaAs and AlAs (100) surfaces are investigated using reflection high-energy electron diffraction along the alternate deposition of Ga or Al and As₄ on the growing surface. Different characteristics are observed for Ga atoms deposited on a GaAs surface and for Al atoms deposited on an AlAs surface. Excess Ga deposition to the GaAs surface produces Ga clusters or droplets on the first Ga layer. They are dissolved very quickly after As₄ deposition to form flat GaAs layers when the number of Ga atoms is closely equal to twice or three times the surface site number. This is not true, however, for Al deposition on AlAs. Different characteristics are also found for Ga and Al atoms deposited on the As-stable GaAs surface. All these results are interpreted in terms of different migration velocities of Ga and Al atoms.