SURFACE-DIFFUSION PROCESSES IN MOLECULAR-BEAM EPITAXIAL-GROWTH OF GAAS AND ALAS AS STUDIED ON GAAS (001)-(111)B FACET STRUCTURES

Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)B and (001) depend strongly on the As flux and are mainly determined by the diffusion of Ga ad-atoms between the two planes. In contrast, the diffusion of Al is found to be almost negligible, irrespective of the As flux. By analyzing the shape of the facet, the diffusion length, lambda, of Ga on a (001) surface is estimated to be about 1 mum at 580-degrees-C, while that of Al is about 0.02 mum. On (111)B, lambda of Ga is found to be several mums. The reflectivity of diffusing Ga atoms is found to be far less than 1 for the (001)-(111)B boundary, and almost unity at facet boundaries where the (111)B side surfaces are bound by the (11BAR0) side walls.