Quantitative analysis of streaks in reflection high-energy electron diffraction: GaAs and AlAs deposited on GaAs(001)

Reflection high-energy electron diffraction (RHEED) has long been considered a qualitative tool for assessing the roughness of a surface and for determining whether thin films are deposited epitaxially. Though this technique is known to be exceedingly surface sensitive, no quantitative statements could be made. In this paper we report measurements of the specular diffraction beam from near-singular GaAs(001) surfaces with submonolayer deposits of GaAs and AlAs. By fitting the shapes of these beams to a kinematic calculation, exact to within the column approximation, we determine the coverages of the surfaces and estimate the average island size in the overlayer. The results show the sensitivity of RHEED to the details of the island or step distribution on the surface. By comparing the AlAs and GaAs profiles it is apparent that Al is much less mobile on the (001) surface than is Ga. Finally we report the observation of surface roughening during the 2×4 to c(4×4) GaAs(001) phase transition.