Morphology of GaAs and Al(x)Ga(1-x)As grown by molecular beam epitaxy.

In this paper the origin of the two major morphological defects that occur in the growth of GaAs and Al(x)Ga(1-x)As by Molecular Beam Epitaxy are discussed. A uniform, fine scale(1000 angstrom period) roughness found on Al(x)Ga(1-x)As wafers grown at certain temperatures is shown to result from the presence of a thin Ga layer that has segregated on the surface during growth. This surface roughness leads to high interfacial recombination velocities at GaAs-Al(x)Ga(1-x)As heterojunctions and strongly degrades heterostructure device performance, especially lasers. Larger (20 micron) but localized (density ~10(4)cm(-2)) oval defects are shown to result from spitting of globules of material from the Group III element effusion cells. The density of these defects is sufficiently low so that the yield of discrete devices is not significantly reduced; however, these defects are likely to be a problem for integrated circuits.