Observations of anomalous droplet formation during the molecular beam epitaxy of AlAs on GaAs (111)B surfaces with an alternating source supply

A unique droplet behavior has been observed during the molecular beam epitaxial growth of AlAs on GaAs (111)B surfaces with an alternating source supply by in situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED) in real time. It has been found that the intermixing of Al and Ga atoms strongly affects droplet formation during the initial four cycles of the growth. The droplet density increases and its size decreases as the growth cycle proceeds, and after the 5th growth cycle, the density and size are almost constant. The surface diffusion lengths of excess group-III atoms in the 1st and 5th cycles are estimated to be about 55 and 3.3 μm, agreeing with those obtained in the homoepitaxial cases of GaAs and AlAs, respectively.