Role of arsenic in the heteroepitaxy of Ge/GaAs

During the heteroepitaxy of Ge on GaAs, arsenic diffuses from the GaAs substrates and hence is present in the Ge epilayer. It has been shown that As is incorporated into the layer but also segregated to the surface. The Ge growth is monitored in situ by laser reflectometry, and it gives the thickness, the growth rate, and the morphology of the layer. It is shown here that a too large surface concentration of As due to intentional doping can block the Ge growth. Atomic force micrographs of the morphological defects (pyramidlike void and large steps) suggest that these defects are due to local segregated excess As concentrations caused by the step advance. It is shown that the density of defects as well as the thickness at which they appear are characterized by the same activation energy of ∼1 eV.